May’s Patch Tuesday haul touches a six-pack of product families

[Update, 2023-05-10: Additional information added about CVE-2023-24932]

Microsoft on Tuesday released patches for 38 vulnerabilities in 6 product families, including 6 Critical-severity issues in Windows and one in SharePoint. As usual, the largest number of addressed vulnerabilities affect Windows, with 27 CVEs. Office follows with 4 CVEs, then SharePoint (3), AV1 Video Extension (2), and Teams and Visual Studio (one each).

At patch time, just two of the issues this month (CVE-2023-29325 and CVE-2023-24932, both Windows) have been publicly disclosed. Microsoft’s updated guidance for CVE-2023-24932 (aka Secure Boot Security Feature Bypass) says this bug has been exploited in the wild by malware called the BlackLotus UEFI bootkit. The company also published additional Secure Boot exploit mitigations that some system administrators may want to take to protect specific systems from BlackLotus; The mitigations, once enabled, are not reversible: In Microsoft’s words, “Even reformatting of the disk will not remove the revocations if they have already been applied.” These mitigations also have a dramatic effect on recovery images, or bootable external media. “After these revocations are applied, the devices will intentionally become unable to start by using recovery or installation media, unless this media has been updated with the security updates released on or after May 9, 2023. This includes both bootable media, such as discs, external drives, network boot recovery, and restore images,” the company writes.

As for the rest, only one other has been detected under exploit in the wild: CVE-2023-29336, an Important-severity elevation-of-privilege issue in Windows. However, Microsoft cautions that eight of the issues addressed are more likely to be exploited in either the latest or earlier versions of the affected product soon (that is, within the next 30 days). Interestingly, Microsoft this month offered no guidance overview on exploitation likelihood in earlier versions versus latest versions for any of the 38 patches, though a few apply only to one or the other.

By popular demand, we are including at the end of this post three appendices listing all the month’s patches, sorted by severity, by predicted exploitability, and by product family.

By the numbers

• Total Microsoft CVEs: 38
• Total advisories shipping in update: 0
• Publicly disclosed: 2
• Exploited: 1
• Severity
  • Critical: 7
  • Important: 31
• Impact
  • Remote code execution: 12
  • Elevation of privilege: 10
  • Information disclosure: 8
  • Denial of service: 5
  • Security feature bypass: 3

Figure 1: Remote code execution issues once again make up the largest portion of May 2023’s patches from Microsoft, but security feature bypass makes a stronger-than-usual swing with three patches

The six product families in the May release:

• Windows: 27
• Office: 4
• SharePoint: 3
• AV1 Video Extension: 2
• Teams: 1
• Visual Studio: 1

Microsoft also acknowledged three Chromium-related CVEs and five GitHub-related CVEs in this month patch-release announcements. The three Chromium-related issues (CVE-2023-29334, CVE-2023-29350, CVE-2023-29354) were patched prior to today’s release, while the five GitHub-related issues (CVE-2023-25652, CVE-2023-25815, CVE-2023-29007, CVE-2023-29011, CVE-2023-29012), all of which affect Visual Studio, were patched today.

Figure 2: Windows patches make up two-thirds of the May 2023 load, and six of seven of the Critical-class issues

Notable May updates

CVE-2023-24941 – Windows Network File System Remote Code Execution Vulnerability

CVE-2023-29325 – Windows OLE Remote Code Execution Vulnerability

Both of these Critical-class RCE patches are thought to be more likely to end up under active exploitation within the next 30 days; worse, both come with fairly detailed installation requirements. System administrators are cautioned to read the instructions very carefully and, in the case of the NFS patch, to be sure that a patch addressing CVE-2022-26937 (released May 2022) is already installed.

CVE-2023-24932 – Secure Boot Security Feature Bypass Vulnerability

As with the previous two patches, this one comes with extra steps: The patch updates Windows Boot Manager, but it’s not enabled by default, so additional steps by the system administrator will be necessary. This patch is related to ongoing attempts to address a vulnerability used by the BlackLotus bootkit. Microsoft described their progress on that process in a standalone post.

CVE-2023-24881 — Microsoft Teams Information Disclosure Vulnerability

Continuing the theme of the Notable Updates this month, this Important-class information disclosure issue takes a bit more attention than usual. First, sysadmins must upgrade to the latest Teams JavaScript SDK library; second, sysadmins must not refer to any domain outside their own control, and must avoid any wildcard domains. System administrators are strongly advised to review Microsoft’s guidance on this patch before proceeding.

CVE-2023-29340 — AV1 Video Extension Remote Code Execution Vulnerability

Finally, this Important-class RCE, one of two addressing AV1 this month, only affects users who installed their extension through the Microsoft Store – and then only if they don’t have auto-updates enabled.

Figure 3: As the year goes on, remote code execution flaws account for the largest number of patches overall and the largest number of critical-severity patches so far

Sophos protections

This table will be updated as individual signatures are finalized.

As you can every month, if you don’t want to wait for your system to pull down Microsoft’s updates itself, you can download them manually from the Windows Update Catalog website. Run the winver.exe tool to determine which build of Windows 10 or 11 you’re running, then download the Cumulative Update package for your specific system’s architecture and build number.

Appendix A: Vulnerability Impact and Severity

This is a list of May’s patches sorted by impact, then sub-sorted by severity. Each list is further arranged by CVE.

Remote Code Execution (12 CVEs)

Elevation of Privilege (10 CVEs)

Information Disclosure (8 CVEs)

Denial of Service (5 CVEs)

Security Feature Bypass (3 CVEs)

Appendix B: Exploitability

This is a list of the May CVEs judged by Microsoft to be more likely to be exploited in the wild within the first 30 days post-release, as well as those already known to be under exploit. Each list is further arranged by CVE.

Appendix C: Products Affected

This is a list of May’s patches sorted by product family, then sub-sorted by severity. Each list is further arranged by CVE.

Windows (27 CVEs)

Office (4 CVEs)

SharePoint (3 CVEs)

AV1 (2 CVEs)

Teams (one CVE)

Visual Studio (one CVE)