Subvert Trust Controls: Code Signing

Adversaries may create, acquire, or steal code signing materials to sign their malware or tools. Code signing provides a level of authenticity on a binary from the developer and a guarantee that the binary has not been tampered with. [1] The certificates used during an operation may be created, acquired, or stolen by the adversary. [2] [3] Unlike Invalid Code Signature, this activity will result in a valid signature.

Code signing to verify software on first run can be used on modern Windows and macOS/OS X systems. It is not used on Linux due to the decentralized nature of the platform. [1]

Code signing certificates may be used to bypass security policies that require signed code to execute on a system.

ID: T1553.002
Sub-technique of:  T1553
Tactic: Defense Evasion
Platforms: Windows, macOS
Data Sources: File: File Metadata
Defense Bypassed: Windows User Account Control
Version: 1.0
Created: 05 February 2020
Last Modified: 10 February 2020

Procedure Examples

ID Name Description
S0504 Anchor

Anchor has been signed with valid certificates to evade detection by security tools.[4]

S0584 AppleJeus

AppleJeus has used a valid digital signature from Sectigo to appear legitimate.[5]

G0016 APT29

APT29 was able to get SUNBURST signed by SolarWinds code signing certificates by injecting the malware into the SolarWinds Orion software lifecycle.[6]

G0096 APT41

APT41 leveraged code-signing certificates to sign malware when targeting both gaming and non-gaming organizations.[7]

S0475 BackConfig

BackConfig has been signed with self signed digital certificates mimicking a legitimate software company.[8]

S0534 Bazar

Bazar has been signed with fake certificates including those appearing to be from VB CORPORATE PTY. LTD.[9]

S0520 BLINDINGCAN

BLINDINGCAN has been signed with code-signing certificates such as CodeRipper.[10]

S0415 BOOSTWRITE

BOOSTWRITE has been signed by a valid CA.[11]

S0144 ChChes

ChChes samples were digitally signed with a certificate originally used by Hacking Team that was later leaked and subsequently revoked.[12][13][14]

S0154 Cobalt Strike

Cobalt Strike can use self signed Java applets to execute signed applet attacks.[15]

G0052 CopyKittens

CopyKittens digitally signed an executable with a stolen certificate from legitimate company AI Squared.[16]

S0527 CSPY Downloader

CSPY Downloader has come signed with revoked certificates.[17]

G0012 Darkhotel

Darkhotel has used code-signing certificates on its malware that are either forged due to weak keys or stolen. Darkhotel has also stolen certificates and signed backdoors and downloaders with them.[18][19]

S0187 Daserf

Some Daserf samples were signed with a stolen digital certificate.[20]

S0377 Ebury

Ebury has installed a self-signed RPM package mimicking the original system package on RPM based systems.[21]

S0091 Epic

Turla has used valid digital certificates from Sysprint AG to sign its Epic dropper.[22]

G0037 FIN6

FIN6 has used Comodo code-signing certificates.[23]

G0046 FIN7

FIN7 has signed Carbanak payloads with legally purchased code signing certificates. FIN7 has also digitally signed their phishing documents, backdoors and other staging tools to bypass security controls.[24][25]

G0093 GALLIUM

GALLIUM has used stolen certificates to sign its tools including those from Whizzimo LLC.[26]

S0168 Gazer

Gazer versions are signed with various valid certificates; one was likely faked and issued by Comodo for "Solid Loop Ltd," and another was issued for "Ultimate Computer Support Ltd."[27][28]

S0342 GreyEnergy

GreyEnergy digitally signs the malware with a code-signing certificate.[29]

S0170 Helminth

Helminth samples have been signed with legitimate, compromised code signing certificates owned by software company AI Squared.[30]

G0072 Honeybee

Honeybee uses a dropper called MaoCheng that harvests a stolen digital signature from Adobe Systems.[31]

S0163 Janicab

Janicab used a valid AppleDeveloperID to sign the code to get past security restrictions.[32]

G0094 Kimsuky

Kimsuky has signed files with the name EGIS CO,. Ltd..[33]

G0065 Leviathan

Leviathan has used stolen code signing certificates to sign malware.[34][35]

S0372 LockerGoga

LockerGoga has been signed with stolen certificates in order to make it look more legitimate.[36]

S0455 Metamorfo

Metamorfo has digitally signed executables using AVAST Software certificates.[37]

G0021 Molerats

Molerats has used forged Microsoft code-signing certificates on malware.[38]

S0284 More_eggs

More_eggs has used a signed binary shellcode loader and a signed Dynamic Link Library (DLL) to create a reverse shell.[23]

S0210 Nerex

Nerex drops a signed Microsoft DLL to disk.[39]

G0040 Patchwork

Patchwork has signed malware with self-signed certificates from fictitious and spoofed legitimate software companies.[8]

S0501 PipeMon

PipeMon, its installer, and tools are signed with stolen code-signing certificates.[40]

G0056 PROMETHIUM

PROMETHIUM has signed code with self-signed certificates.[41]

S0262 QuasarRAT

A QuasarRAT .dll file is digitally signed by a certificate from AirVPN.[42]

S0148 RTM

RTM samples have been signed with a code-signing certificates.[43]

G0091 Silence

Silence has used a valid certificate to sign their primary loader Silence.Downloader (aka TrueBot).[44]

S0491 StrongPity

StrongPity has been signed with self-signed certificates.[41]

G0039 Suckfly

Suckfly has used stolen certificates to sign its malware.[45]

S0559 SUNBURST

SUNBURST was digitally signed by SolarWinds from March - May 2020.[6]

G0092 TA505

TA505 has signed payloads with code signing certificates from Thawte and Sectigo.[46][47][48]

S0266 TrickBot

TrickBot has come with a signed downloader component.[4]

G0044 Winnti Group

Winnti Group used stolen certificates to sign its malware.[49]

G0102 Wizard Spider

Wizard Spider has used Digicert code-signing certificates for some of its malware.[50]

Mitigations

This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of system features.

Detection

Collect and analyze signing certificate metadata on software that executes within the environment to look for unusual certificate characteristics and outliers.

References

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  3. Shinotsuka, H. (2013, February 22). How Attackers Steal Private Keys from Digital Certificates. Retrieved March 31, 2016.
  4. Dahan, A. et al. (2019, December 11). DROPPING ANCHOR: FROM A TRICKBOT INFECTION TO THE DISCOVERY OF THE ANCHOR MALWARE. Retrieved September 10, 2020.
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  12. Miller-Osborn, J. and Grunzweig, J.. (2017, February 16). menuPass Returns with New Malware and New Attacks Against Japanese Academics and Organizations. Retrieved March 1, 2017.
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  1. MSTIC. (2019, December 12). GALLIUM: Targeting global telecom. Retrieved January 13, 2021.
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  3. Kaspersky Lab's Global Research & Analysis Team. (2017, August 30). Introducing WhiteBear. Retrieved September 21, 2017.
  4. Cherepanov, A. (2018, October). GREYENERGY A successor to BlackEnergy. Retrieved November 15, 2018.
  5. ClearSky Cybersecurity. (2017, January 5). Iranian Threat Agent OilRig Delivers Digitally Signed Malware, Impersonates University of Oxford. Retrieved May 3, 2017.
  6. Sherstobitoff, R. (2018, March 02). McAfee Uncovers Operation Honeybee, a Malicious Document Campaign Targeting Humanitarian Aid Groups. Retrieved May 16, 2018.
  7. Thomas. (2013, July 15). New signed malware called Janicab. Retrieved July 17, 2017.
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