Andy Ful
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- Dec 23, 2014
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Inside Microsoft's plan to kill PPLFault (by Gabriel Landau)
Inside Microsoft's plan to kill PPLFault — Elastic Security Labs
In this research publication, we'll learn about upcoming improvements to the Windows Code Integrity subsystem that will make it harder for malware to tamper with Anti-Malware processes and other important security features.
www.elastic.co
Forget vulnerable drivers - Admin is all you need — Elastic Security Labs
Bring Your Own Vulnerable Driver (BYOVD) is an increasingly popular attacker technique whereby a threat actor brings a known-vulnerable signed driver alongside their malware, loads it into the kernel, then exploits it to perform some action within the kernel that they would not otherwise be able...
www.elastic.co
On September 1, 2023, Microsoft released a new build of Windows Insider Canary, version 25941. Insider builds are pre-release versions of Windows that include experimental features that may or may not ever reach General Availability (GA). Build 25941 includes improvements to the Code Integrity (CI) subsystem that mitigate a long-standing issue that enables attackers to load unsigned code into Protected Process Light (PPL) processes.
The PPL mechanism was introduced in Windows 8.1, enabling specially-signed programs to run in such a way that they are protected from tampering and termination, even by administrative processes. The goal was to keep malware from running amok — tampering with critical system processes and terminating anti-malware applications. There is a hierarchy of PPL “levels,” with higher-privilege ones immune from tampering by lower-privilege ones, but not vice-versa. Most PPL processes are managed by Microsoft but members of the Microsoft Virus Initiative are allowed to run their products at the less-trusted Anti-Malware PPL level.
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Exploitation
In September 2022, Gabriel Landau from Elastic Security filed VULN-074311 with MSRC, notifying them of two zero-day vulnerabilities in Windows: one admin-to-PPL and one PPL-to-kernel. Two exploits for these vulnerabilities were provided named PPLFault and GodFault, respectively, along with their source code. These exploits allow malware to bypass LSA protection, terminate or blind EDR software, and modify kernel memory to tamper with core OS behavior - all without the use of any vulnerable drivers. See this article for more details on their impact.
The admin-to-PPL exploit PPLFault leverages the fact that page hashes are not validated for PPL and employs the Cloud Filter API to violate immutability assumptions of files backing SEC_IMAGE sections. PPLFault uses paging to inject code into a DLL loaded within a PPL process running as WinTcb-Light, the most privileged form of PPL. The PPL-to-kernel exploit GodFault first uses PPLFault to get WinTcb-Light code execution, then exploits the kernel’s trust of WinTcb-Light processes to modify kernel memory, granting itself full read-write access to physical memory.
Though MSRC declined to take any action on these vulnerabilities, the Windows Defender team has shown interest. PPLFault and GodFault were released at Black Hat Asia in May 2023 alongside a mitigation to stop these exploits called NoFault.
Mitigation
On September 1, 2023, Microsoft released build 25941 of Windows Insider Canary. This build adds a new check to the memory manager function MiValidateSectionCreate which enables page hashes for all images that reside on remote devices.
