Vulnerability Report

CVE-2026-50257

Title: Use-after-free in X.Org X server miSyncDestroyFence()

Auth Bypass

Proof Of Concept

No public PoC currently indexed for CVE-2026-50257.

CWE Category CWE-416

Published Date Jun 05, 2026

Modified Date Jul 27, 2026

Exploit Status Not Found

Score 7.8 CVSS v3.1

Exploit Probability (EPSS)

0.14%

Vulnerability Summary

CVE-2026-50257: 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.

Impacted Vendors

Reference Links

https://access.redhat.com/security/cve/CVE-2026-50257 https://bugzilla.redhat.com/show_bug.cgi?id=2485382 https://gitlab.freedesktop.org/xorg/xserver/-/commit/f5abfb61994471023d8c6470428c8e30c411cc0b https://lists.x.org/archives/xorg-announce/2026-June/003702.html https://redhat.atlassian.net/browse/PSIRTSUPT-16950

CVSS v3.1

Source Entity [email protected]

Severity HIGH

7.8

Attack Vector

LOCAL

Complexity

LOW

Privileges

N/A

Interaction

NONE

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

UNCHANGED

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

CVSS v3.1

Source Entity 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

Severity HIGH

7.8

Attack Vector

LOCAL

Complexity

LOW

Privileges

N/A

Interaction

NONE

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

UNCHANGED

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

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2026-50257 Exploits & PoCs (Proof Of Concept)

No public PoCs found in our database for this CVE.

July 27, 2026 MODIFIED

Vulnerability data updated via NVD.

July 27, 2026 MODIFIED

Vulnerability data updated via NVD.

July 27, 2026 MODIFIED

Vulnerability data updated via NVD.

July 27, 2026 MODIFIED

Vulnerability data updated via NVD.

July 27, 2026 MODIFIED

Vulnerability data updated via NVD.

July 15, 2026 MODIFIED

Vulnerability data updated via NVD.

July 13, 2026 MODIFIED

Vulnerability data updated via NVD.

July 13, 2026 MODIFIED

Vulnerability data updated via NVD.

July 13, 2026 MODIFIED

Vulnerability data updated via NVD.

July 09, 2026 MODIFIED

Vulnerability data updated via NVD.

July 09, 2026 MODIFIED

Vulnerability data updated via NVD.

July 08, 2026 MODIFIED

Vulnerability data updated via NVD.

July 08, 2026 MODIFIED

Vulnerability data updated via NVD.

July 08, 2026 MODIFIED

Vulnerability data updated via NVD.

July 07, 2026 MODIFIED

Vulnerability data updated via NVD.

July 07, 2026 MODIFIED

Vulnerability data updated via NVD.

June 30, 2026 MODIFIED

Vulnerability data updated via NVD.

June 25, 2026 MODIFIED

Vulnerability data updated via NVD.

June 24, 2026 MODIFIED

Vulnerability data updated via NVD.

June 22, 2026 MODIFIED

Vulnerability data updated via NVD.

June 18, 2026 MODIFIED

Vulnerability data updated via NVD.

June 08, 2026 MODIFIED

Vulnerability data updated via NVD.

June 05, 2026 MODIFIED

Vulnerability data updated via NVD.

June 05, 2026 MODIFIED

Vulnerability data updated via NVD.

Attack Vector Matrix

Access Vector LOCAL

Complexity LOW

Privileges N/A

Interaction NONE

CVSS Vector String


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

Affected Stack

No specific products linked.