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Microsoft Now Says SPNEGO Extended Negotiation Security Vulnerability (CVE-2022-37958) is Critical

Updated on 2022-12-15: CVE-2022-37958

Valentina Palmiotti, a security researcher at IBM’s X-Force Red, has released more details about CVE-2022-37958, a vulnerability in the Windows SPNEGO protocol that Microsoft patched back in September. A video demonstration of the bug is here. The tl;dr here is below. Long story short, it’s really bad!

“The vulnerability is in the SPNEGO Extended Negotiation (NEGOEX) Security Mechanism, which allows a client and server to negotiate the choice of security mechanism to use. This vulnerability is a pre-authentication remote code execution vulnerability impacting a wide range of protocols. It has the potential to be wormable.”

“Unlike the vulnerability (CVE-2017-0144) exploited by EternalBlue and used in the WannaCry ransomware attacks, which only affected the SMB protocol, this vulnerability has a broader scope and could potentially affect a wider range of Windows systems due to a larger attack surface of services exposed to the public internet (HTTP, RDP, SMB) or on internal networks. This vulnerability does not require user interaction or authentication by a victim on a target system.”

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Overview: Microsoft Now Says SPNEGO Extended Negotiation Security Vulnerability is Critical

Microsoft has reclassified a vulnerability they patched in September as critical. The vulnerability in the Simple and Protected GSSAPI Negotiation Mechanism (SPNEGO) Extended Negotiation Security Mechanism (CVE-2022-37958) was initially described as an information disclosure issue. Now it has been found that the flaw could be exploited to allow remote execution of arbitrary code, prompting Microsoft to reclassify its severity.


  • Common mechanisms that can be used to exploit the vulnerability are SMB, HTTP, and RDP. While you’re no longer exposing SMB and RDP to the Internet, you are likely exposing HTTP. Don’t panic: make sure the September update was rolled out to those servers. Microsoft included the update in the monthly rollup for their OSes, as well as their security specific update patch set.


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