Pierluigi Paganini May 17, 2021

A security researcher has published a working proof-of-concept exploit code for a wormable Windows IIS server vulnerability tracked as CVE-2021-31166.

Microsoft Patch Tuesday for May 2021 security updates addressed 55 vulnerabilities in Microsoft including a critical HTTP Protocol Stack Remote Code Execution vulnerability tracked as CVE-2021-31166. The flaw could be exploited by an unauthenticated attacker by sending a specially crafted packet to a targeted server utilizing the HTTP Protocol Stack (http.sys) to process packets.

This stack is used by the Windows built-in IIS server, which means that it could be easily exploited if the server is enabled. The flaw is wormable and affects different versions of Windows 10, Windows Server 2004 and Windows Server 20H2.

The security researcher Axel Souchet has published over the weekend a proof-of-concept exploit code for the wormable flaw that impacted Windows IIS.

The PoC exploit code allows to crash an unpatched Windows system running an IIS server, it does not implement worming capabilities.

Anyway attackers could start triggering the vulnerability in the wild, the PoC code could be improved to be actively exploited.

The public availability of the PoC exploit code is another good reason to apply Microsoft Patch Tuesday for May 2021 security updates as soon as possible.

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Pierluigi Paganini

(SecurityAffairs – hacking, RCE)

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