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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
2026-08-05
Advisory published
2026-06-05
Advisory updated
2026-08-05

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.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-50257 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-50257

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-50257 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-50257

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.