CVE-2021-31955 — Windows 10 20h2
MEDIUMCVE-2021-31955 is a medium-severity (CVSS 5.5) CWE-497 vulnerability in microsoft windows 10 20h2. It is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.
Windows Kernel Information Disclosure Vulnerability
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2021-11-03. Federal agencies were required to remediate by 2021-11-17.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2021-31955.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-31955 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Counts from FIRST.org, log-scaled.
Description
Windows Kernel Information Disclosure Vulnerability
Affected Products
windows 10 20h2microsoftwindows 10 21h1microsoftwindows 10 1809microsoftwindows 10 1909microsoftwindows 10 2004microsoftwindows server 20h2microsoftResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Windows Kernel Information Disclosure Vulnerability
Windows Kernel Information Disclosure Vulnerability
Windows Kernel Information Disclosure Vulnerability
Windows Kernel Information Disclosure Vulnerability
Windows Kernel Information Disclosure Vulnerability
Windows Kernel Information Disclosure Vulnerability
Detection & mitigation playbook
Vendor / applianceDetect
Inventory every microsoft windows 10 20h2 deployment and check each version against the affected-products list above.
Fix
Apply the microsoft windows 10 20h2 security patch or hotfix for CVE-2021-31955 on the affected version, following the vendor advisory for your exact build.
Workarounds
Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.
Frequently Asked Questions
Is CVE-2021-31955 being exploited in your environment?
Detect and block the exploit chain at execution, on systems you cannot patch yet.