Patch Tuesday - July 2023

Last updated at Thu, 10 Aug 2023 20:52:42 GMT

Microsoft is addressing 130 vulnerabilities this July Patch Tuesday, including five zero-day vulnerabilities, and eight further critical remote code execution (RCE) vulnerabilities. Overall, it’s safe to say that this is a busier Patch Tuesday than the past couple of months. Note that the total count of vulnerabilities reported no longer includes any Edge-on-Chromium fixes.

Office zero-day maldoc vuln: no patch, no problem

Surprisingly, there is no patch yet for one of the five zero-day vulnerabilities. Microsoft is actively investigating publicly-disclosed Office RCE CVE-2023-36884, and promises to update the advisory as soon as further guidance is available. Exploitation requires the victim to open a specially crafted malicious document, which would typically be delivered via email.

A Microsoft Security Research Centre (MSRC) blog post links exploitation of this vulnerability with Storm-0978, Microsoft’s designation for a cybercriminal group based out of Russia also tracked across the wider industry under the name RomCom. MSRC suggests that RomCom / Storm-0978 is operating in support of Russian intelligence operations. The same threat actor has also been associated with ransomware attacks targeting a wide array of victims.

Defenders who are understandably unsettled by the lack of immediate patches for CVE-2023-36884 should consult the multiple mitigation options on the advisory. Microsoft claims that assets with Defender for Office 365 are already protected. Further options include an existing optional Defender for Endpoint Attack Surface Reduction (ASR) rule to prevent Office from creating child processes, and a registry modification to disable the vulnerable cross-protocol file navigation. The registry option might be the most straightforward option for organizations without a mature Defender program, but Microsoft does warn that certain use cases relying on the functionality would be impacted if this mitigation is deployed.

There are broad similarities to last year’s Follina vulnerability, which was discussed publicly for over two weeks starting late May 2023 before Microsoft patched it on June 14th as part of Patch Tuesday. While it’s possible that a patch for CVE-2023-36884 will be issued as part of next month’s Patch Tuesday, Microsoft Office is deployed just about everywhere, and this threat actor is making waves; admins should be ready for an out-of-cycle security update for CVE-2023-36884.

The menu of mitigation options here should offer something for every Microsoft shop, but it will come as something of a relief that Microsoft is offering patches for the four other zero-day vulnerabilities mentioned in this month’s Security Update Guide.

MSHTML, Windows Error Reporting: zero-day elevation of privilege vulns

CVE-2023-32046 describes a vulnerability in the MSHTML browser rendering engine which would allow an attacker to act with the same rights as the exploited user account. Successful exploitation requires the victim to open a specially-crafted malicious file, typically delivered either via email or a web page. Assets where Internet Explorer 11 has been fully disabled are still vulnerable until patched; the MSHTML engine remains installed within Windows regardless of the status of IE11, since it is used in other contexts (e.g. Outlook).

A separate vulnerability in the Windows Error Reporting Service allows elevation to the Administrator role via abuse of Windows performance tracing. To exploit CVE-2023-36874, an attacker must already have existing local access to an asset, so this vulnerability will most likely make up part of a longer exploit chain.

SmartScreen & Outlook: zero-day security feature bypass vulns

Rounding out this month’s zero-day vulnerabilities are two security feature bypass flaws. CVE-2023-32049 allows an attacker to formulate a URL which will bypass the Windows SmartScreen “Do you want to open this file?” dialog. Previous SmartScreen bypasses have been exploited extensively, not least for no-notice delivery of ransomware.

Broadly similar is CVE-2023-35311, which describes a bypass of the Microsoft Outlook Security Notice dialog via a specially-crafted URL.

Windows RRAS: critical RCEs

Eight further critical RCE vulnerabilities are also patched, including three related vulnerabilities in the Windows Routing and Remote Access Service (RRAS) with CVSS v3 base score of 9.8 (CVE-2023-35365, CVE-2023-35366, and CVE-2023-35367). In each case, an attacker can send specially-crafted packets to vulnerable assets to achieve RCE. Happily, RRAS is not installed or configured by default, but admins with RRAS-enabled Windows Server installations will undoubtedly want to prioritize remediation.

SharePoint: critical RCEs

Anyone responsible for on-prem SharePoint should patch to avoid a variety of potential impacts from exploitation of CVE-2023-33157 and CVE-2023-33160, including information disclosure and editing, as well as reduced availability of the targeted environment. While both of these vulnerabilities require that an attacker already be authenticated as a user with at least Site Member privileges, this isn’t necessarily much of a defense, since this is the lowest standard permission group with the least privileges other than the read-only Site Visitor role, and will typically be widely granted. Microsoft assesses exploitation as more likely for both of these.

Windows core components: critical RCEs

The remainder of this month’s critical RCE patches target flaws in the Windows Layer-2 Bridge Network Driver (CVE-2023-35315), and usual suspects Windows Message Queuing (CVE-2023-32057) and Windows PGM (CVE-2023-35297).

Windows Remote Desktop: security feature bypass

CVE-2023-35352 will be of interest to anyone running an RDP server. Although the advisory is short on detail, an attacker could bypass certificate or private key authentication when establishing a remote desktop protocol session. Although the CVSS v3 base score of 7.5 falls short of the critical band, this is only because Microsoft has scored this vulnerability as having no impact on either confidentiality or availability, probably because the scoring is against the RDP service itself rather than whatever may be accessed downstream; this seems like a case where CVSS cannot fully capture the potential risk, and Microsoft’s Security Update Severity Rating System does rank this vulnerability as critical.

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Microsoft Office Windows ESU vulnerabilities

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