CVE-2026-50257 | Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: use-after-free in misyncdestroyfence()

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: 2026-06-05 Last update: 2026-06-08 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-50257 is rated Low Risk (31.8/100): CVSS High severity, with low exploitation likelihood (EPSS 0.01%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-50257

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-05 — 0.01% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-50257

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.8 3.1 HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 5.9 [email protected]

Weakness enumeration for CVE-2026-50257

GitHub Security Advisory for CVE-2026-50257

GHSA-5p7p-jgvj-4v95 · Severity: high — A use-after-free flaw was found in the X.Org X server and Xwayland in miSyncDestroyFence(). A...

OS Trackers for CVE-2026-50257

vendor priority summary link
debian not yet assigned CVE-2026-50257 not yet assigned priority: Debian including 2 source packages (xorg-server, xwayland), 9 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 6, resolved 3. https://security-tracker.debian.org/tracker/CVE-2026-50257
suse high CVE-2026-50257 severity important: SUSE including 3 source package names (xorg-x11-server, xorg-x11-server-extra, xorg-x11-server-sdk), 12 product×package rows across 5 product lines (SUSE Linux Enterprise Server 12 SP4-LTSS, SUSE Linux Enterprise Server 15 SP1-LTSS, … (5 product lines)): Known Not Affected 12. https://www.suse.com/security/cve/CVE-2026-50257/
ubuntu medium CVE-2026-50257 medium priority: Ubuntu including 7 source packages (xorg, xorg-hwe-16.04, …), 46 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): needs-triage 17, DNE 16, not-affected 12, released 1. https://ubuntu.com/security/CVE-2026-50257

Affected software / configurations for CVE-2026-50257

Vendor Product Version Raw CPE
x.org x_server < 21.1.23 cpe:2.3:a:x.org:x_server:*:*:*:*:*:*:*:*
x.org xwayland < 24.1.12 cpe:2.3:a:x.org:xwayland:*:*:*:*:*:*:*:*
redhat enterprise_linux 7.0 cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
redhat enterprise_linux 9.0 cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:*
redhat enterprise_linux 10.0 cpe:2.3:o:redhat:enterprise_linux:10.0:*:*:*:*:*:*:*

References for CVE-2026-50257

cvelogic Threat Intelligence