# Taking Advantage of PE Metadata, or How To Complete your Favorite Threat Actor’s Sample Collection

Daniel Lunghi
daniel_lunghi@trendmicro.com

Trend Micro

**Abstract. In this paper, we will show some common techniques that**
we leveraged in a real case investigation that started with one SysUpdate
sample found in December 2020, and ended with dozens of samples from
the same malware family, dating back to March 2015. SysUpdate is a
malware family that has been attributed to the Iron Tiger threat actor in
the past. Other malware families from the same threat actor were found,
and the result of the investigation has been published in the Trend Micro
blog [4]. The goal of the current paper is to discuss some of the techniques
that proved useful to gather related samples, with detailed examples. It
is complementary with the investigation presented at SSTIC in 2020 [9].

This investigation started when Talent Jump [1] company handed us a
malware sample that they found in December 2020 in a gambling company.
That gambling company had already been targeted in July 2019, in what
we called Operation DRBControl [5]. Our goals were to find if the sample
belonged to a known malware family, a known threat actor, and if it was
related to the previous campaign.

## 1 Sample analysis

Four files were initially sent to us, and the code analysis showed that
a fifth file was involved:
— dlpumgr32.exe, a legitimate signed file that is part of the DESlock+
product
— DLPPREM32.DLL, a malicious DLL sideloaded [1] by dlpumgr32.exe
that loads and decodes DLPPREM32.bin
— DLPPREM32.bin, a shellcode that decompresses and loads a launcher
in memory
— data.res, an encrypted file decoded by the launcher that contains
two SysUpdate versions: one for a 32-bit architecture and another
for a 64-bit architecture

1. http://www.talent-jump.com/EN_index.html


-----

2 Taking Advantage of PE Metadata

— config.res, an encrypted file decoded by the launcher which
contains the SysUpdate command-and-control (C&C) address
The config.res file was not directly available to us, but we could
confirm by analyzing a process dump that it contained the C&C IP address.
The code analysis showed that the file is deleted right after being read.

**Fig. 1. SysUpdate sample loading process**

A quick analysis of the unobfuscated code reveals some interesting
RTTI class names, which help figuring some of the malware features:

— CMShell
— CMFile
— CMCapture
— CMServices
— CMProcess
— CMPipeServer
— CMPipeClient


-----

M. Lunghi 3

## 2 Malware family identification

The process of obtaining unobfuscated code from the packed files
is off-topic, but as seen on figure 1, the unobfuscated code is only
present in memory. After dumping the unobfuscated code, our goal was
to identify the malware family, if known. We found a hardcoded useragent, Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36
(KHTML, like Gecko) Chrome/34.0.1847.116 Safari/537.36, which
was mentioned in an article written by Dell SecureWorks [17] in February
27, 2019 on the Bronze Union threat actor, also known as Emissary Panda,
APT27, LuckyMouse or Iron Tiger [12]. The article mentions two malware
families, HyperBro [2] and SysUpdate. We were familiar with HyperBro,
as we encountered it during our investigation on Operation DRBControl [6] in 2019, so we could discard it. We found another article [14]
listing the features of the SysUpdate malware family, and they matched
the behavior of the in-memory launcher displayed in figure 1. Thanks to
it, we confidently assumed that this malware belonged to the SysUpdate
family.

## 3 Pivoting on metadata

The two previously listed articles [14,17] provided indicators of compromise (IOC) of old SysUpdate samples that we could retrieve. A quick
analysis showed that their loading process was quite similar, involving a
legitimate signed file loading a malicious DLL, which unpacks a binary
file in-memory. However, no launcher nor additional files were involved.

**Fig. 2. Loading process of a SysUpdate sample found in NCC blog [14]**

**3.1** **Filename**

We noticed the sys.bin.url filename has been used in both cases.
This was our first pivot, and searching for this filename followed by relevant


-----

4 Taking Advantage of PE Metadata

**Fig. 3. Loading process of a SysUpdate sample found in Dell SecureWorks blog [17]**

keywords (APT, malware) returned sandbox results, but no new samples.
Issuing the same query [2] in the Virus Total platform returned 7 results,
some of which were unknown to us. Searching for their MD5 hashes in
search engines, we found another article [8] written in Farsi language
which described the same malware, and contained further IOCs.
In that list, we noticed another legitimate binary being abused by the
attacker for side-loading a malicious DLL: PYTHON33.dll. In that case,
the DLL unpacked a binary file named PYTHON33.hlp. A new search [3] on
this filename returned four samples and a new technical analysis [13] of
our malware. We also found a security bulletin [3] from the UAE national
CERT dated June 13, 2019 which mentioned a malware family named
HyperSSL. After analysis, it turned out it was the same malware family,
and thus HyperSSL could be considered an alias of SysUpdate.
In addition to pivoting on filenames for packed payloads, which can be
changed by the attacker at any moment, we noticed that the threat actor
tended to reuse the same legitimate executables to side-load its malicious
DLL libraries. As the attacker did not control the code of such signed
legitimate binaries, he could not change the names of the side-loaded
libraries, and thus we could leverage that behavior to hunt for malicious
DLL libraries based on their name. As an example, we could search for
libraries named PYTHON33.dll, but we had to filter the results, because a
simple query returned 166 results. We removed corrupt samples, but there
were still 99 samples left. After analyzing malicious DLL files from the
attacker, we noticed their size was always less than 100 Kb, whereas the
official Python library was heavier than a megabyte. By adding a filter on
the file size [4], we obtained only five files, which we could analyze manually.
It turned out they were all related to the SysUpdate malware family.

2. https://www.virustotal.com/gui/search/name:sys.bin.url/files
3. https://www.virustotal.com/gui/search/name:python33.hlp/files
4. https://www.virustotal.com/gui/search/name:PYTHON33.dllsize:100KbNOTtag:corrupt/files


-----

M. Lunghi 5

At this point, simple queries on filenames learned us that our threat
actor has targeted Middle-East countries in the past (Iran, UAE), among
which governmental entities, and we expanded our IOC list, not only with
samples but also with infrastructure. We also saw multiple reports of
malware families and TTPs related to our threat actor.

**3.2** **Imphash**

“Imphash” or “Import hashing” is a method invented by FireEye and
published [11] in 2014. The general idea is that the Import Address Table
(IAT), which is built at compilation time, changes depending on which
order the functions are placed in the source code. Thus, when a significant
amount of functions are imported and called in a malware’s source code,
its IAT has a fingerprint unique enough to allow for correlations. Multiple
tools [5] exist to generate this hash. In our case, this method worked pretty
well on the malicious DLLs compiled by our threat actor. For example,
a search [6] query on the imphash 509a3352028077367321fbf20f39f6d9
returned three files related to Iron Tiger. Other platforms, such as Malware
Bazaar, allow for similar search queries [7] through their API.
It is also possible to build a Yara rule that matches on files with a
specific imphash:

**import "pe"**
**rule** **sysupdate_dll_imphash**
{

**meta** :

**author = "Daniel** Lunghi"
**description = "Matches** Iron Tiger ’s SysUpdate DLLs from 2019"
**purpose = "Show an** example of imphash Yara rule for SSTIC 2021
conference "
**condition :**

**uint16 (0) ==0 x5a4d** **and // "MZ" header**
**pe** . imphash ()== "509 a3352028077367321fbf20f39f6d9 "
}

**3.3** **PE RICH Header**

The RICH header is added by the Microsoft compiler to files in the
Portable Executable (PE) format. It has been first documented [15] in
2010. It embeds many information, such as the compiler’s version, up to

5. https://github.com/Neo23x0/ImpHash-Generator
6. https://www.virustotal.com/gui/search/imphash:
509a3352028077367321fbf20f39f6d9/files
7. https://bazaar.abuse.ch/api/#imphash


-----

6 Taking Advantage of PE Metadata

the build number. Researchers have taken advantage [10] of this header
for the last couple of years, because it sometimes bring useful correlations. The general idea is that a similar building environment should
produce a similar header, which could help finding binaries that have
been compiled in the same machine. Some public tools [8] generate a MD5
hash of the RICH header, which can then be used in a Yara rule, or in
malware repositories that support it. As an example, searching for the
hash 5503d2d1e505a487cbc37b6ed423081f in Virus Total returns three
files, which are all related to our threat actor.
The following Yara rule matches those samples:

**import "pe"**
**import "hash"**
**rule** **sysupdate_richheader**
{

**meta** :

**author = "Daniel** Lunghi"
**description = "Matches** Iron Tiger ’s SysUpdate DLLs from 2018"
**purpose = "Show an** example of RICH header Yara rule for SSTIC
2021 conference "
**condition :**

**uint16 (0) ==0 x5a4d** **and // "MZ" header**
**hash** . **md5** ( **pe** . rich_signature . clear_data )== "5503

d2d1e505a487cbc37b6ed423081f "
}

However, it is important to note that this header is ignored when
running an executable, and thus, it can be altered without any impact
on the code execution. In 2018, it has been proven [7] that a threat actor
purposefully modified the RICH header of an executable to match the
header of another threat actor.

**3.4** **Stolen certificates**

PE executables can be signed using the Microsoft Authenticode technology. The purpose is to identify the publisher of the code and guarantee
the code integrity. Authenticode relies on x509 certificates and certification
authorities. Some threat actors compromise software companies to steal
the private key that allows them to generate a valid signature for their own
malicious executables. This might confuse some security solutions or young
analysts that might flag signed code as non malicious. From a defender
stand point, it is useful to check for compromised certificates, as usually a
threat actor will sign more than one executable with a stolen certificate. In
the case of Iron Tiger, we found that DLL inicore_v2.3.30.dll reported

8. https://gist.github.com/fr0gger/44ef948d5f129a183b4d44d3e867e097


-----

M. Lunghi 7

by Palo Alto [16] was signed by a certificate stolen from the company
Kepware Technologies. Searching for its serial number [9] or thumbprint
10 in Virus Total returns six results, which are all related to the SysUpdate malware family. Malware Bazaar provides two keywords related to
certificates, serial_number and issuer_cn, which are self-explanatory.
The following Yara rule matches samples signed by the stolen certificate:

**import "pe"**
**rule** **sysupdate_compromised_kepware_certificate**
{

**meta** :

**author = "Daniel** Lunghi"
**description = "Matches** Iron Tiger ’s files from 2018 signed by a
stolen certificate from Kepware Technologies "
**purpose = "Show an** example of a Yara rule handling certificates
for SSTIC 2021 conference "
**condition :**

**uint16 (0) ==0 x5a4d** **and // "MZ" header**
**for** **any i in (0 .. pe** . number_of_signatures ) : (
_//_ _thumbprint_ _and_ _serial_ _must_ _be_ _lower_ _case_
**pe** . signatures [ **i** ]. serial == "0d:02: f1 :24: c1 :64:96:22:57:06: f4:
ed:d3:8d:a6 :96"
**or pe** . signatures [ **i** ]. thumbprint == "
fa89c0cbfce8d745ef3b2f72312077799e69df72 "
)
}

Note that the stolen certificate has been revoked by the certification
authority, so the malicious files’ signature is not valid anymore.

**3.5** **TLSH**

Multiple “fuzzy hashing” algorithms exist that intend to match
similar files automatically. They usually split the original file in blocks of
variable length, and then make a hash of the different blocks. The most
popular fuzzy hashing algorithm is SSDeep. However, results on compiled
code are usually not good. Of all the fuzzy hashing algorithms that we
looked at, TLSH was the one that gave better results for correlation.
Results should still be taken with caution. As an example, TLSH hash

T112F21A0172A28477E1AE2A3424B592725D7F7C416AF040CB3F9916FA9FB16D0DA3C367
returned 223 results in Virus Total, and while many of them were
related to our threat actor, many of them were not, and simply

9. https://www.virustotal.com/gui/search/signature:
0D02F124C16496225706F4EDD38DA696/file
10. https://www.virustotal.com/gui/search/signature:
FA89C0CBFCE8D745EF3B2F72312077799E69DF72/files


-----

8 Taking Advantage of PE Metadata

had a similar structure. On the other hand, searching for the hash

T17A634B327C97D8B7E1D97AB858A2DA12152F250059F588C9BF7043E70F2A6509E37F0E
returned only two results, and both were related to our threat actor. Note
that Malware Bazaar also allows to search for TLSH hash in its API [11].

## 4 Conclusion

The goal of this short paper was to present some techniques that
defenders can leverage when investigating a breach to gather additional
information and IOC about the threat actor. It is complementary with the
talk [9] presented at SSTIC in 2020, this time focusing on PE metadata.
By using these techniques in a recent investigation, we started from a
single unknown sample and found more than thirty samples from the same
malware family, around 15 C&C IP addresses, multiple reports discussing
the same threat actor and detailing its targets and Tactics, Techniques and
Procedures (TTPs). It shows the importance of public research containing
IOC, which helped us to identify the malware family. We could also
compare our sample to previous versions of the same malware and spot
the structural changes.
We hope that by showing examples taken from a real case investigation,
it will help young researchers to apply these techniques to their own
investigations.

## References

1. Mitre ATT&CK. DLL Side-Loading. https://attack.mitre.org/techniques/
T1073/.

2. Mitre ATT&CK. HyperBro. https://attack.mitre.org/software/S0398/.

3. CERT.ae. ADV-19-27-Advanced Notification of Cyber Threats against Family of
Malware Giving Remote Access to Computers. https://www.tra.gov.ae/assets/
mTP39Tp6.pdf.aspx, 2019.

4. K. Lu D. Lunghi. Iron Tiger APT Updates Toolkit With Evolved SysUpdate Malware. https://www.trendmicro.com/en_us/research/21/d/iron-tiger-aptupdates-toolkit-with-evolved-sysupdate-malware-va.html, 2021.

5. K. Lu J. Yaneza D. Lunghi, C. Pernet. Uncovering a Cyberespionage
Campaign Targeting Gambling Companies in Southeast Asia. https:
//www.trendmicro.com/vinfo/us/security/news/cyber-attacks/operationdrbcontrol-uncovering-a-cyberespionage-campaign-targeting-gamblingcompanies-in-southeast-asia, 2020.

11. https://bazaar.abuse.ch/api/#tlsh


-----

M. Lunghi 9

6. K. Lu J. Yaneza D. Lunghi, C. Pernet. Uncovering DRBControl - Inside the
Cyberespionage Campaign Targeting Gambling Operations. https://documents.
trendmicro.com/assets/white_papers/wp-uncovering-DRBcontrol.pdf, 2020.

7. GReAT. The devil’s in the Rich header. https://securelist.com/the-devilsin-the-rich-header/84348/, 2018.

8. Kamiran. APT27 HackerTeam Analyse. https://www.kamiran.asia/documents/
APT27_HackerTeam_Analyse.pdf, 2019.

9. D. Lunghi. Pivoter tel Bernard, ou comment monitorer des attaquants négligents. https://www.sstic.org/2020/presentation/pivoter_tel_bernard_ou_
comment_monitorer_des_attaquants_ngligents/, 2020.

10. P. Kálnai M. Poslušný. Rich Headers: leveraging this mysterious artifact of the
PE format. https://www.virusbulletin.com/virusbulletin/2020/01/vb2019paper-rich-headers-leveraging-mysterious-artifact-pe-format/, 2019.

11. Mandiant. Tracking Malware with Import Hashing. https://www.fireeye.
com/blog/threat-research/2014/01/tracking-malware-import-hashing.html,
2014.

12. Mitre. Threat Group-3390. https://attack.mitre.org/groups/G0027/, 2017.

13. Norfolk. Emissary Panda DLL Backdoor. https://norfolkinfosec.com/
emissary-panda-dll-backdoor/, 2019.

14. N. Pantazopoulos. Emissary Panda – A potential new malicious tool.
https://research.nccgroup.com/2018/05/18/emissary-panda-a-potentialnew-malicious-tool/, 2018.

15. D. Pistelli. Microsoft’s Rich Signature (undocumented). https://www.ntcore.
com/files/richsign.htm, 2010.

16. T. Lancaster R. Falcone. Emissary Panda Attacks Middle East Government
SharePoint Servers. https://unit42.paloaltonetworks.com/emissary-pandaattacks-middle-east-government-sharepoint-servers/, 2019.

17. Counter Threat Unit™(CTU) researcher team. A Peek into BRONZE
UNION’s Toolbox. https://www.secureworks.com/research/a-peek-intobronze-unions-toolbox, 2019.


-----