CVE-2026-50257

HIGH

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.

CVSS v3.1 Score

7.8
HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack Vector
LOCAL
Complexity
LOW
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Published: 6/5/2026Modified: 6/8/2026

Related Intelligence (2)

CRITICALZero Day

Patch Tuesday - June 2026

Microsoft is publishing 200 vulnerabilities on June 2026 Patch Tuesday . Microsoft is not aware of exploitation in the wild for any of these vulnerabilities, and is aware of public disclosure for three. This is similar to last month’s Patch Tuesday, however several of last month’s vulnerabilities ended up on CISA KEV in the days following their publication. So far this month, Microsoft has provide

CVE-2026-33825CVE-2026-45585
Rapid7
HIGHVulnerability

NVD HIGH: CVE-2026-50257 — A use-after-free flaw was found in the X.Org X server and Xwayland in miSyncDest...

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 privileg

CVE-2026-50257
NIST NVD

References (5)

https://access.redhat.com/security/cve/CVE-2026-50257Third Party Advisoryhttps://bugzilla.redhat.com/show_bug.cgi?id=2485382Issue TrackingThird Party Advisoryhttps://gitlab.freedesktop.org/xorg/xserver/-/commit/f5abfb61994471023d8c6470428c8e30c411cc0bPatchhttps://lists.x.org/archives/xorg-announce/2026-June/003702.htmlMailing ListThird Party Advisoryhttps://redhat.atlassian.net/browse/PSIRTSUPT-16950Permissions Required