Hackers Exploit Windows Policy Loophole to Forge Kernel-Mode Driver Signatures

A Microsoft Windows plan loophole has been noticed getting exploited mostly by indigenous Chinese-speaking threat actors to forge signatures on kernel-manner drivers.

“Actors are leveraging several open-supply resources that alter the signing date of kernel method drivers to load malicious and unverified motorists signed with expired certificates,” Cisco Talos mentioned in an exhaustive two-portion report shared with The Hacker News. “This is a main menace, as accessibility to the kernel gives complete obtain to a technique, and thus full compromise.”

Pursuing liable disclosure, Microsoft has taken ways to block all certificates to mitigate the menace.

Driver signature enforcement, which involves kernel-manner drivers to be digitally signed with a certification from Microsoft’s Dev Portal, is a vital line of protection against malicious motorists, which could be most likely weaponized to evade security answers, tamper with procedure processes, and maintain persistence.

The new weak point discovered by Cisco Talos can make it feasible to forge signatures on kernel-mode drivers, thereby permitting Windows certificate policies to be bypassed.

This is created achievable due to an exception carved out by Microsoft to preserve compatibility, which permits cross-signed drivers if they were being “signed with an end-entity certification issued prior to July 29 2015 that chains to a supported cross-signed [certificate authority].”

“The third exception creates a loophole that permits a newly compiled driver to be signed with non-revoked certificates issued prior to or expired in advance of July 29, 2015, provided that the certificate chains to a supported cross-signed certification authority,” the cybersecurity corporation explained.

As a consequence, a driver signed in this method will not be prevented from remaining loaded on a Windows machine, thus enabling risk actors to consider benefit of the escape clause to deploy hundreds of destructive, signed drivers with out distributing them to Microsoft for verification.

These rogue drivers are deployed making use of signature timestamp forging software these as HookSignTool and FuckCertVerifyTimeValidity, which have been publicly obtainable given that 2019 and 2018, respectively.

HookSignTool has been obtainable via GitHub considering that January 7, 2020, though FuckCertVerifyTimeValidity was to start with fully commited to the code hosting services on December 14, 2018.

“HookSignTool is a driver signature forging resource that alters the signing date of a driver through the signing system via a blend of hooking into the Windows API and manually altering the import desk of a legit code signing tool,” Cisco Talos spelled out.

Especially, it consists of hooking to the CertVerifyTimeValidity perform, which verifies the time validity of a certificate, to alter the signing timestamp in the course of execution.

“This tiny venture stops the signtool from verifing [sic] cert time validity and allow you signal your bin with out-of-date cert without having modifying technique time manually,” the GitHub webpage for FuckCertVerifyTimeValidity reads.

“It set up hook into crypt32!CertVerifyTimeValidity and make it generally return and make kernel32!GetLocalTime return what you want as you can insert “-fuckyear 2011″ to signtool’s command line to indication a cert from calendar year 2011.”

That claimed, pulling off a productive forgery calls for a non-revoked code signing certificate that was issued prior to July 29, 2015, alongside with the certificate’s non-public critical and passphrase.

Cisco Talos said it uncovered above a dozen code-signing certificates with keys and passwords contained in a PFX file hosted on GitHub in a forked repository of FuckCertVerifyTimeValidity. It is really not right away distinct how these certificates ended up acquired.

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What is actually far more, it has been noticed that HookSignTool has been applied to re-indicator cracked drivers in get to bypass digital rights management (DRM) integrity checks, with an actor named “Juno_Jr” releasing a cracked edition of PrimoCache, a legit application caching resolution, in a Chinese application cracking discussion board on November 9, 2022.

“In the cracked model […], the patched driver was re-signed with a certification at first issued to ‘Shenzhen Luyoudashi Technology Co., Ltd.,’ which is contained in the PFX file on GitHub,” Talos researchers reported. “This capacity to resign a cracked driver gets rid of a considerable roadblock when making an attempt to bypass DRM checks in a signed driver.”

That’s not all. HookSignTool is also remaining used by a beforehand undocumented driver recognized as RedDriver to forge its signature timestamp. Energetic considering that at least 2021, it functions as a driver-based browser hijacker that leverages the Windows Filtering Platform (WFP) to intercept browser traffic and reroute it to localhost (127…1).

The target browser is preferred at random from a really hard-coded listing containing the procedure names of lots of well known Chinese language browsers like Liebao, QQ Browser, Sogou, and UC Browser, as very well as Google Chrome, Microsoft Edge, and Mozilla Firefox.

The top goal of this browser site visitors redirection is not very clear, while it goes without the need of expressing that these kinds of a capability could be abused to tamper with browser visitors at the packet amount.

RedDriver infection chains begin with the execution of a binary named “DnfClientShell32.exe,” which, in change, initiates encrypted communications with a command-and-management (C2) server to down load the malicious driver.

“RedDriver was likely created by remarkably competent danger actors as the finding out curve for creating destructive motorists is steep,” Cisco Talos explained. “Whilst the threat appears to target indigenous Chinese speakers, the authors are most likely Chinese speakers as properly.”

“The authors also shown a familiarity or expertise with application enhancement lifecycles, a different ability established that involves earlier growth experience.”

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Some components of this report are sourced from:
thehackernews.com