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Description

A use-after-free flaw was found in the X.Org X server and Xwayland in miSyncDestroyFence(). A client that sets up multiple fence triggers can trigger a use-after-free function pointer call. An attacker would connect to the X server to set up a fence and await that fence, then a second X connection destroys the fence, causing the use-after-free. This may be used to crash the server, or for privilege escalation if the X server runs as root.

PUBLISHED Reserved 2026-06-04 | Published 2026-06-05 | Updated 2026-06-09 | Assigner redhat




HIGH: 7.8CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Problem types

Use After Free

Product status

Default status
affected

Default status
unknown

Default status
affected

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affected

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affected

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affected

Default status
affected

Timeline

2026-05-15:Reported to Red Hat.
2026-06-02:Made public.

Credits

Upstream acknowledges Anonymous (Trend Micro Zero Day Initiative) as the original reporter.

References

access.redhat.com/security/cve/CVE-2026-50257 vdb-entry

bugzilla.redhat.com/show_bug.cgi?id=2485382 (RHBZ#2485382) issue-tracking

gitlab.freedesktop.org/...61994471023d8c6470428c8e30c411cc0b

lists.x.org/archives/xorg-announce/2026-June/003702.html

redhat.atlassian.net/browse/PSIRTSUPT-16950

cve.org (CVE-2026-50257)

nvd.nist.gov (CVE-2026-50257)

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