A zero-click vulnerability in Windows allows stealing NTLM credentials

Researchers shared technical details about a flaw in Windows MSHTML platform, tracked as CVE-2023-29324, that could be abused to bypass security protections.

Cybersecurity researchers have shared details about a now-patched security flaw, tracked as CVE-2023-29324 (CVSS score: 6.5), in Windows MSHTML platform.

An attacker can exploit the vulnerability by crafting a malicious URL that would evade zone checks.

“An attacker can craft a malicious URL that would evade zone checks, resulting in a limited loss of integrity and availability of the victim machine” reads the advisory published by Microsoft.

This vulnerability affects all supported versions of Microsoft Windows, it was reported by the Security Researcher Ben Barnea from Akamai Technologies.

Microsoft addressed the vulnerability with the release of Patch Tuesday security updates for May 2023.

Barnea explained that the issue causes the Windows API function MapUrlToZone to incorrectly think that a remote path is a local one. The problem stems from the complex handling of paths in Windows.

MapUrlToZone calls the function CreateUri which incorrectly converts the path ‘\\.\UNC\\Akamai.com\file.wav’ to ‘/.//UNC//Akamai.com/file.wav’.

“MapUrlToZone is commonly used as a security measure. In particular, it was used to mitigate the critical Outlook vulnerability CVE-2023-23397 patched in the March Patch Tuesday.” reads the analysis published by Barnea. “An unauthenticated attacker on the internet could use the vulnerability to coerce an Outlook client to connect to an attacker-controlled server. This results in NTLM credentials theft. It is a zero-click vulnerability, meaning it can be triggered with no user interaction.”

Microsoft Threat Intelligence observed a Russian threat actor exploiting the CVE-2023-23397 flaw in targeted attacks against several organizations in the European government, transportation, energy, and military sectors, for approximately a year.

“This vulnerability is yet another example of patch scrutinizing leading to new vulnerabilities and bypasses. Specifically for this vulnerability, the addition of one character allows for a critical patch bypass.” concludes the expert.

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Pierluigi Paganini

(SecurityAffairs – hacking, Windows MSHTML)