#Security Vulnerability

**How could an attacker exploit this vulnerability?** In most situations, an unauthenticated attacker could send a specially crafted packet to a targeted server utilizing the HTTP Protocol Stack (http.sys) to process packets. **Is this wormable?** Yes. Microsoft recommends prioritizing the patching of affected servers.

**What configurations or versions could be at risk from this vulnerability?** This bypass could affect any Hyper-V configurations that are using Router Guard. **What is the exposure if the vulnerability was bypassed?** Certain packets that would normally be blocked or dropped could be processed. This could allow an attacker to bypass set policy, potentially influencing router paths.

**What information could be disclosed through this vulnerability?** An attacker could potentially read small portions of heap memory.

**How could an attacker exploit this vulnerability?** An authenticated attacker could run a specially crafted application on a vulnerable Hyper-V guest to exploit this vulnerability. **What privileges could an attacker gain?** An attacker who successfully exploited this vulnerability could potentially interact with processes of another Hyper-V guest hosted on the same Hyper-V host.

**What is the scope of this security update?** This update resolves an elevation of privilege vulnerability specific to Active Directory Domain Services environments with incoming trusts. Prior to this update, an attacker could elevate privileges across the trust boundary under certain conditions.

**Is the Preview Pane an attack vector for this vulnerability?** No, the Preview Pane is not an attack vector.

**Is the Preview Pane an attack vector for this vulnerability?** No, the Preview Pane is not an attack vector.

**How could this vulnerability affect my system** A crafted image file could cause a crash in Explorer during browsing of the directory containing the file. **How do I get the updated app?** The Microsoft Store will automatically update affected customers. Alternatively, customers can get the update immediately; see here for details. It is possible for customers to disable automatic updates for the Microsoft Store. The Microsoft Store will not automatically install this update for those customers. **My system is in a disconnected environment; is it vulnerable?** Customers using the Microsoft Store for Business and Microsoft Store for Education can get this update through their organizations. **How can I check if the update is installed?** If your device manufacturer preinstalled this app, package versions **1.0.43421.0** and later contain this update. If you purchased this app from the Microsoft Store, package versions **1.0.43422.0** and later contain this update. You can ch...

**What type of information could be disclosed by this vulnerability?** The type of information that could be disclosed if an attacker successfully exploited this vulnerability is uninitialized memory.

**Why is this a MITRE Corporation CVE?** CVE-2021-36976 is regarding a vulnerability in the libarchive open source library which is used by Windows. The January 2022 Windows Security Updates include the most recent version of this library which addresses the vulnerability and others. Please see libarchive CVEs for more information regarding all of the vulnerabilities that have been addressed.