CVE-2026-83515 — Microsoft Windows 10 21h2
MEDIUMCVE-2026-83515 is a medium-severity (CVSS 6.5) CWE-908 vulnerability in microsoft windows 10 21h2. A fix is available — see the affected versions and patch details below.
Use of uninitialized resource in RPC Runtime allows an unauthorized attacker to disclose information over a network.
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-83515.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Description
Use of uninitialized resource in RPC Runtime allows an unauthorized attacker to disclose information over a network.
Affected Products
windows 10 21h2microsoftwindows 10 22h2microsoftwindows 10 1607microsoftwindows 10 1809microsoftwindows 11 23h2microsoftwindows 11 24h2microsoftDetection & mitigation playbook
Vendor / applianceDetect
Inventory every microsoft windows 10 21h2 deployment and check each version against the affected-products list above.
Fix
Apply the microsoft windows 10 21h2 security patch or hotfix for CVE-2026-83515 on the affected version, following the vendor advisory for your exact build.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.
Frequently Asked Questions
Is CVE-2026-83515 being exploited in your environment?
Detect and block the exploit chain at execution, on systems you cannot patch yet.