Use-after-free in X.Org X server and Xwayland SyncChangeCounter()
CVE-2026-50261 is a use-after-free vulnerability in the XSYNC component of the X.Org X server and Xwayland, specifically in SyncChangeCounter(). The flaw occurs when a client sets up multiple SyncCounters and those counters are destroyed through a second client connection while they are being changed. This creates a stale reference/use-after-free condition during counter handling. According to the provided advisory context, 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
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Impact
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Mitigation
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Remediation
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Exploits
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No public exploit code observed for this vulnerability.
Affected products & vendors
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Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
6 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.
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The version that knows your environment.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.