Two Microsoft Windows bugs under attack, one in Secure Boot with a manual fix • The Register

Patch Tuesday May’s Patch Tuesday brings some good and some bad news, and if you’re a glass-half-full type, you’d lead off with Microsoft’s relatively low number of security fixes: a mere 38.

Your humble vulture, however, is a glass-half-empty-and-who-the-hell-drank-my-whiskey kind of bird, so instead of looking on the bright side, we’re looking at the two Microsoft bugs that have already been found and exploited by miscreants. Plus a third vulnerability, which has been publicly disclosed. We’d suggest patching these three stat.

Six of the 38 vulnerabilities are deemed “critical” because they allow remote code execution.

The two that are under active exploit, at least according to Microsoft, are CVE-2023-29336, a Win32k elevation of privilege vulnerability; and CVE-2023-24932, a Secure Boot security feature bypass vulnerability, which was exploited by the BlackLotus bootkit to infect Windows machines. Interestingly enough, BlackLotus abused CVE-2023-24932 to defeat a patch Microsoft issued last year that closed another bypass vulnerability in Secure Boot. Thus Redmond fixed a hole in Secure Boot, and this malware abused a second bug, CVE-2023-24932, to get around that.

CVE-2023-29336 is a 7.8-out-of-10 rated flaw in the Win32k kernel-mode driver that can be exploited to gain system privileges on Windows PCs. 

“This type of privilege escalation is usually combined with a code execution bug to spread malware,” Zero Dan Initiative’s Dustin Childs said. “Considering this was reported by an AV company, that seems the likely scenario here.” 

Redmond credited Avast bug hunters Jan Vojtešek, Milánek, and Luigino Camastra with finding and disclosing the bug.

Time to boot out a threat

Meanwhile, CVE-2023-24932 received its own separate Microsoft Security Response Center (MSRC) advisory and configuration guidance, which Redmond says is necessary to “fully protect against this vulnerability.”

“This vulnerability allows an attacker to execute self-signed code at the Unified Extensible Firmware Interface (UEFI) level while Secure Boot is enabled,” MSRC warned. “This is used by threat actors primarily as a persistence and defense evasion mechanism.”

If also noted, however,…