Lazarus hackers exploited Windows zero-day to gain Kernel privileges

North Korean menace actors referred to as the Lazarus Group exploited a flaw within the Windows AppLocker driver (appid.sys) as a zero-day to gain kernel-level entry and switch off safety instruments, permitting them to bypass noisy BYOVD (Bring Your Own Vulnerable Driver) strategies.

This exercise was detected by Avast analysts, who promptly reported it to Microsoft, main to a repair for the flaw, now tracked as CVE-2024-21338, as a part of the February 2024 Patch Tuesday. However, Microsoft has not marked the flaw as being exploited as a zero-day.

Avast studies that Lazarus exploited CVE-2024-21338 to create a learn/write kernel primitive in an up to date model of its FudModule rootkit, which ESET first documented in late 2022. Previously, the rootkit abused a Dell driver for BYOVD assaults.

The new model of FudModule options important enhancements in stealth and performance, together with new and up to date strategies for evading detection and turning off safety protections like Microsoft Defender and CrowdStrike Falcon.

Moreover, by retrieving many of the assault chain, Avast found a beforehand undocumented distant entry trojan (RAT) utilized by Lazarus, which the safety agency promised to share extra particulars about at BlackHat Asia in April.

Lazarus 0-day exploitation

The malware exploited a vulnerability in Microsoft’s ‘appid.sys’ driver, a Windows AppLocker element that gives utility whitelisting capabilities.

Lazarus exploits it by manipulating the Input and Output Control (IOCTL) dispatcher within the appid.sys driver to name an arbitrary pointer, tricking the kernel into executing unsafe code, thus bypassing safety checks.

Direct syscalls used in the exploit
Direct syscalls used within the exploit (Avast)

The FudModule rootkit, constructed inside the similar module because the exploit, executes direct kernel object manipulation (DKOM) operations to flip off safety merchandise, cover malicious actions, and keep persistence on the breached system.

The focused safety merchandise are AhnLab V3 Endpoint Security, Windows Defender, CrowdStrike Falcon, and the HitmanPro anti-malware resolution.

Avast noticed new stealth options and expanded capabilities within the new rootkit model, like the power to suspect processes protected by Protected Process Light (PPL) by manipulating deal with desk entries, selective and focused disruption by way of DKOM, enhancements in tampering with Driver Signature Enforcement and Secure Boot, and extra.

Avast notes that this new exploit tactic marks a major evolution within the menace actor’s kernel entry capabilities, permitting them to launch stealthier assaults and persist on compromised programs for longer intervals.

Rootkit's main function executing individual techiques
Rootkit’s principal perform executing particular person techiques (Avast)

The solely efficient safety measure is to apply the February 2024 Patch Tuesday updates as quickly as doable, as Lazarus’ exploitation of a Windows built-in driver makes the assault significantly difficult to detect and cease.

YARA guidelines to assist defenders detect exercise linked to the most recent model of the FudModule rootkit might be discovered right here.

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