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Microsoft fixed two zero-day vulnerabilities in April 2024 Patch Tuesday, but they didn’t label them as such at first. CVE-2024-26234 is a vulnerability that involves a malicious driver being signed with a valid Microsoft Hardware Publisher Certificate. It was discovered by Sophos X-Ops in December 2023 and reported by team lead Christopher Budd.
This malicious file was labeled as “Catalog Authentication Client Service” by “Catalog Thales,” likely an attempt to impersonate Thales Group. However, further investigation revealed that it was previously bundled with a marketing software called LaiXi Android Screen Mirroring.’
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While Sophos couldn’t verify the authenticity of LaiXi software, Budd says they’re confident the file is a malicious backdoor.
“Just as we did in 2022, we immediately reported our findings to the Microsoft Security Response Center. After validating our discovery, the team at Microsoft has added the relevant files to its revocation list (updated today as part of the usual Patch Tuesday cycle; see CVE-2024-26234),” Budd said.
Sophos’ findings support information from a January report by cybersecurity company Stairwell and a tweet by reverse engineering expert Johann Aydinba.
Redmond has updated the advisory for CVE-2024-26234, confirming that it has been exploited and publicly disclosed.
In July 2023 and December 2022, Sophos discovered more harmful drivers that had been signed using valid WHCP certificates. However, instead of assigning CVE-IDs like they do now, Microsoft released security advisories for those incidents.
MotW bypass exploited in malware attacks:
Microsoft silently patched another zero-day vulnerability today. This vulnerability, tracked as CVE-2024-29988, is related to a security feature bypass in SmartScreen prompt. The vulnerability is caused by a weakness in the protection mechanism.
CVE-2024-29988 is a bypass for the CVE-2024-21412 flaw and was reported by Peter Girnus of Trend Micro’s Zero Day Initiative, as well as by Dmitrij Lenz and Vlad Stolyarov from Google’s Threat Analysis Group.
Dustin Childs, ZDI’s Head of Threat Awareness, identified it as a tool used in attacks to install malware on specific Windows systems. The tool is able to avoid detection by EDR/NDR and bypass the Mark of the Web (MotW) feature.
“This vulnerability is related to CVE-2024-21412, which was discovered by ZDI threat researchers in the wild and first addressed in February,” Childs told BleepingComputer.
“The first patch did not completely resolve the vulnerability. This update addresses the second part of the exploit chain. Microsoft did not indicate they were patching this vulnerability, so it was a (welcome) surprise when the patch went live.”
The Water Hydra group also used a different vulnerability to target forex and stock trading communities on New Year’s Eve.
CVE-2024-21412 was a bypass for another Defender SmartScreen vulnerability called CVE-2023-36025. This vulnerability was fixed in November 2023 but was used as a zero-day to distribute Phemedrone malware.
Microsoft released security updates for 150 vulnerabilities in April 2024. Out of these, 67 were remote code execution bugs.
Source: Microsoft, Bleepingcomputer
