# MAR-10288834-3.v1 – North Korean Trojan: PEBBLEDASH

**us-cert.gov/ncas/analysis-reports/ar20-133c**

## Notification

This report is provided "as is" for informational purposes only. The Department of Homeland Security (DHS) does not provide any warranties of an
information contained herein. The DHS does not endorse any commercial product or service referenced in this bulletin or otherwise.

This document is marked TLP:WHITE--Disclosure is not limited. Sources may use TLP:WHITE when information carries minimal or no foreseeab
accordance with applicable rules and procedures for public release. Subject to standard copyright rules, TLP:WHITE information may be distribute
For more information on the Traffic Light Protocol (TLP), see http://www.us-cert.gov/tlp.

## Summary

Description

This Malware Analysis Report (MAR) is the result of analytic efforts between the Department of Homeland Security (DHS), the Federal Bureau of
the Department of Defense (DoD). Working with U.S. Government partners, DHS, FBI, and DoD identified Trojan malware variants used by the N
government. This malware variant has been identified as PEBBLEDASH. The U.S. Government refers to malicious cyber activity by the North Kor
HIDDEN COBRA. For more information on HIDDEN COBRA activity, visit https[:]//www[.]us-cert.gov/hiddencobra.

FBI has high confidence that HIDDEN COBRA actors are using malware variants in conjunction with proxy servers to maintain a presence on vict
further network exploitation. DHS, FBI, and DoD are distributing this MAR to enable network defense and reduce exposure to North Korean gover
activity.

This MAR includes malware descriptions related to HIDDEN COBRA, suggested response actions and recommended mitigation techniques. Use
should flag activity associated with the malware and report the activity to the Cybersecurity and Infrastructure Security Agency (CISA) or the FBI C
and give the activity the highest priority for enhanced mitigation.

This report looks at a full-featured beaconing implant. This sample uses FakeTLS for session authentication and for network encoding utilizing RC
to download, upload, delete, and execute files; enable Windows CLI access; create and terminate processes; and perform target system enumera
[For a downloadable copy of IOCs, see MAR-10288834-3.v1.stix.](https://www.us-cert.gov/sites/default/files/publications/MAR-10288834-3.v1.stix.xml)

Submitted Files (1)

aab2868a6ebc6bdee5bd12104191db9fc1950b30bcf96eab99801624651e77b6 (D2DE01858417FA3B580B3A95857847...)

IPs (1)

112.217.108.138

## Findings

**aab2868a6ebc6bdee5bd12104191db9fc1950b30bcf96eab99801624651e77b6**

Tags

rootkittrojan

Details

**Name** D2DE01858417FA3B580B3A95857847D5

**Size** 167937 bytes

**Type** PE32 executable (GUI) Intel 80386, for MS Windows

**MD5** d2de01858417fa3b580b3a95857847d5

**SHA1** 2c879a1d4b6334c59ac5f11c2038d273d334befe

**SHA256** aab2868a6ebc6bdee5bd12104191db9fc1950b30bcf96eab99801624651e77b6

**SHA512** 220c74af533f4565c4d6f0b4a4ac37c4c6e6238eba22d976a8c28889381a7d920e29077287144ec71f60e5a0b3f3780b6c688e34b8b63

**ssdeep** 3072:LH+Sv//jDG2TJVw2URyELc1VVA9Rznhy7i+2JYI3mX2nwvjbtdKQ:qSn/jDGtUEWgE792nmX2Eb3

**Entropy** 6.131834

Antivirus

**Ahnlab** Trojan/Win32.Akdoor

**Avira** TR/Fuery.eipis

**BitDefender** Trojan.GenericKD.5147779

**ESET** a variant of Win32/NukeSped.G trojan


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**Emsisoft** Trojan.GenericKD.5147779 (B)

**Filseclab** Rootkit.Agent.eki.zwum.mg

**Ikarus** Trojan.Win32.NukeSped

**NANOAV** Trojan.Win32.Fuery.ephjck

**Symantec** Trojan Horse

**VirusBlokAda** BScope.Trojan.Dynamer

**Zillya!** Trojan.NukeSped.Win32.4

YARA Rules

rule CISA_3P_10135536_02 : rc4_key_2

{
meta:
Author = "CISA Trusted Third Party"

Incident = "10135536"

Date = "2018-04-19"
Actor = "Hidden Cobra"

Category = "n/a"

Family = "n/a"

Description = "n/a"

strings:

$s1 = { c6 ?? ?? 79 c6 ?? ?? e1 c6 ?? ?? 0a c6 ?? ?? 5d c6 ?? ?? 87 c6 ?? ?? 7d c6 ?? ?? 9f c6 ?? ?? f7 c6 ?? ?? 5d c6 ?? ?? 12 c6 ?
?? ?? 65 c6 ?? ?? ac c6 ?? ?? e3 c6 ?? ?? 25 }

$s2 = { c7 ?? ?? 79 e1 0a 5d c7 ?? ?? 87 7d 9f f7 c7 ?? ?? 5d 12 2e 11 c7 ?? ?? 65 ac e3 25 }

condition:

(uint16(0) == 0x5A4D and uint16(uint32(0x3c)) == 0x4550) and any of them

}

ssdeep Matches

**100** d620d88dfe1dbc0b407d0c3010ff18963e8bb1534f32998322f5a16746a1d0a6

PE Metadata

**Compile Date** 2017-05-10 08:32:48-04:00

**Import Hash** 244a466b5f07e9bef21f34a777edebc2

PE Sections

**MD5** **Name** **Raw Size** **Entropy**

735665170a22a6b60e78ba64be8f525a header 4096 0.685116

03861d6eb2f7ce7eb5a2c20dae40d62b .text 135168 6.307038

bfcf9ded9905d8f7d6afdcf03737a029 .rdata 12288 5.094334

16cb2fb46f6bf6aaae5d9daf38d0f5d4 .data 12288 5.001095

14f705208660fe080429a2fc23a6c181 .rsrc 4096 0.405655

Packers/Compilers/Cryptors

Microsoft Visual C++ v6.0

Relationships

aab2868a6e... Connected_To 112.217.108.138

Description

The sample performs dynamic dynamic link library (DLL) importing and application programming interface (API) lookups using LoadLibrary and G
obfuscated strings in an attempt to hide it’s usage of network functions. The sample obfuscates strings used for API lookups using a custom XOR
script to decrypt the obfuscated strings is given below.

--Begin Python3 script-
# key = 69 A7 DD 86 0A 67 78 77 A6 78 9A DA 78 68 A7 78

def decode_string(enc, key):

dec = b''


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g ( ( ))
# rotate key:
# [0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f] -> [x,0,1,2,3,4,5,6,7,8,9,a,b,c,d,e]
# where x=(key[0]^key[2])^(key[6]&key[f])
for j in range(15, 0, -1):
key[j] = key[j-1]
key[0] = (key[0] ^ key[2]) ^ (key[6] + key[15])

dec += bytes([enc[i] ^ key[15]])
return dec
--End Python3 script-
The sample obfuscates its callback descriptors (IP address and ports) using a different custom XOR algorithm. A Python3 script to decrypt the ob
below.

--Begin Python3 script-# key = 5E 85 41 FD 0C 37 57 71 D5 51 5D E3 B5 55 62 20
#   C1 30 96 D3 77 4C 23 13 84 8B 63 5C 48 32 2C 5B
#   94 8F 3A 26 79 E2 6B 94 45 D1 6F 51 24 8F 86 72
#   C8 D3 8D C1 C0 D3 88 56 84 B3 91 E2 B2 24 64 24
def decode_callback_descriptors(enc, key):
dec = b''
for i in range(len(enc)):
dec += bytes([enc[i] ^ key[(i + 0x1378 + len(enc)) % 0x40] ^ 0x59])
return dec
--End Python3 script-
The sample utilizes a “FakeTLS” scheme in an attempt to obfuscate its network communications. It picks a random Uniform Resource Locator (UR
to use in the TLS certificate. The sample and the command and control (C2) externally appear to perform a standard TLS authentication, howeve
are filled with random data from rand().

--Begin C2-112.217.108.138:443
--End C2-
Once the FakeTLS handshake is complete, all further packets use a FakeTLS header, followed by RC4 encrypted data.

--Begin packet structure-17 03 01 <2 Byte data length> <RC4 encrypted data>
RC4 Key: 79 E1 0A 5D 87 7D 9F F7 5D 12 2E 11 65 AC E3 25
--End packet structure-
The sample then waits for commands from the C2.
Screenshots

**Figure 1 - List of certificate URLs used in the TLS certificate.**


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**Figure 2 - The implant contains the commands displayed in the table.**

**112.217.108.138**

Tags

command-and-control

Relationships

112.217.108.138 Connected_From aab2868a6ebc6bdee5bd12104191db9fc1950b30bcf96eab99801624651e77b6

Description

The malware attempts to connect to the IP address.

## Relationship Summary

aab2868a6e... Connected_To 112.217.108.138

112.217.108.138 Connected_From aab2868a6ebc6bdee5bd12104191db9fc1950b30bcf96eab99801624651e77b6

## Mitigation

The following Snort rule can be used to detect the FakeTLS RC4 encrypted command packets:

//Detects the FakeTLS RC4 encrypted command packets
// that use no arguments (i.e. nextlen = 0)

alert tcp any any -> any any (msg:"Malware Detected"; pcre:" /\x17\x03\x01\x00\x08.\x20\x59\x2c/"; rev:1; sid:99999999;)
## Recommendations

CISA recommends that users and administrators consider using the following best practices to strengthen the security posture of their organizatio
configuration changes should be reviewed by system owners and administrators prior to implementation to avoid unwanted impacts.

Maintain up-to-date antivirus signatures and engines.
Keep operating system patches up-to-date.
Disable File and Printer sharing services. If these services are required, use strong passwords or Active Directory authentication.
Restrict users' ability (permissions) to install and run unwanted software applications. Do not add users to the local administrators group unl
Enforce a strong password policy and implement regular password changes.
Exercise caution when opening e-mail attachments even if the attachment is expected and the sender appears to be known.
Enable a personal firewall on agency workstations, configured to deny unsolicited connection requests.
Disable unnecessary services on agency workstations and servers.
Scan for and remove suspicious e-mail attachments; ensure the scanned attachment is its "true file type" (i.e., the extension matches the file
Monitor users' web browsing habits; restrict access to sites with unfavorable content.
Exercise caution when using removable media (e.g., USB thumb drives, external drives, CDs, etc.).


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p g
Maintain situational awareness of the latest threats and implement appropriate Access Control Lists (ACLs).

Additional information on malware incident prevention and handling can be found in National Institute of Standards and Technology (NIST) Specia
**"Guide to Malware Incident Prevention & Handling for Desktops and Laptops".**

## Contact Information

CISA continuously strives to improve its products and services. You can help by answering a very short series of questions about this product at t
[https://us-cert.gov/forms/feedback/](https://us-cert.gov/forms/feedback/)

## Document FAQ

**What is a MIFR? A Malware Initial Findings Report (MIFR) is intended to provide organizations with malware analysis in a timely manner. In most**
will provide initial indicators for computer and network defense. To request additional analysis, please contact CISA and provide information regar
analysis.

**What is a MAR? A Malware Analysis Report (MAR) is intended to provide organizations with more detailed malware analysis acquired via manua**
To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

**Can I edit this document? This document is not to be edited in any way by recipients. All comments or questions related to this document should**
[CISA at 1-888-282-0870 or soc@us-cert.gov.](http://10.10.0.46/mailto:soc@us-cert.gov)

**Can I submit malware to CISA? Malware samples can be submitted via three methods:**

Web: [https://malware.us-cert.gov](https://malware.us-cert.gov/)
E-Mail: [submit@malware.us-cert.gov](http://10.10.0.46/mailto:submit@malware.us-cert.gov)
FTP: ftp.malware.us-cert.gov (anonymous)

CISA encourages you to report any suspicious activity, including cybersecurity incidents, possible malicious code, software vulnerabilities, and ph
[Reporting forms can be found on CISA's homepage at www.us-cert.gov.](http://www.us-cert.gov/)

## Revisions

May 12, 2020: Initial Version

[This product is provided subject to this Notification and this](https://www.us-cert.gov/privacy/notification) [Privacy & Use policy.](https://www.dhs.gov/privacy-policy)

**Please share your thoughts.**

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