Use-after-free in X.Org X server/Xwayland miSyncDestroyFence()
CVE-2026-50257 is a use-after-free vulnerability in the XSYNC subsystem of the X.Org X server and Xwayland, specifically in miSyncDestroyFence(). A client can set up multiple fence triggers and await a fence on one X connection, while a second client connection destroys that fence. This results in a use-after-free function pointer call during fence handling. The issue affects X.Org X server versions prior to 21.1.23 and Xwayland versions prior to 24.1.12.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
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Remediation
Patch, then assume compromise.
Exploits
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No public exploit code observed for this vulnerability.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.