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CVE-2026-50257 Red Hat CVE debrief

CVE-2026-50257 is a HIGH severity vulnerability in X.Org X server and Xwayland. A use-after-free flaw was found 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.

Vendor
Red Hat
Product
Red Hat Enterprise Linux 10
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-05
Original CVE updated
2026-06-08
Advisory published
2026-06-05
Advisory updated
2026-06-08

Who should care

Administrators and users of X.Org X server and Xwayland, particularly those with the X server running as root, should be aware of this vulnerability.

Technical summary

The vulnerability exists in the X.Org X server and Xwayland in the miSyncDestroyFence() function. A use-after-free flaw can be triggered by a client setting up multiple fence triggers, leading to a potential crash or privilege escalation.

Defensive priority

HIGH

Recommended defensive actions

  • Apply patches or updates from the vendor as soon as possible.
  • Restrict access to the X server to trusted users only.
  • Monitor for any suspicious activity or anomalies in the X server logs.

Evidence notes

The CVE-2026-50257 vulnerability was published on 2026-06-05T12:16:38.907Z and modified on 2026-06-08T16:45:56.703Z. The CVSS score is 7.8 with a HIGH severity rating.

Official resources

CVE-2026-50257 was publicly disclosed on 2026-06-05.