X.org X11 Server SyncChangeCounter use after free

CVSS Meta Temp Score
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CTI Interest Score
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7.8$0-$5k0.00

Summaryinfo

A vulnerability has been found in X.org X11 Server and classified as critical. Affected is the function SyncChangeCounter. This manipulation causes use after free. This vulnerability is tracked as CVE-2026-50261. The attack is restricted to local execution. No exploit exists.

Detailsinfo

A vulnerability was found in X.org X11 Server (the affected version unknown). It has been declared as critical. Affected by this vulnerability is the function SyncChangeCounter. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

A use-after-free flaw was found in the X.Org X server and Xwayland in SyncChangeCounter(). A client that sets up multiple SyncCounters can trigger a use-after-free when destroying those counters via a second client connection while changing those counters. This may be used to crash the server, or for privilege escalation if the X server runs as root.

The advisory is shared at access.redhat.com. This vulnerability is known as CVE-2026-50261 since 06/04/2026. The exploitation appears to be easy. An attack has to be approached locally. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 06/06/2026).

The vulnerability scanner Nessus provides a plugin with the ID 318744 (Linux Distros Unpatched Vulnerability : CVE-2026-50261), which helps to determine the existence of the flaw in a target environment.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the databases at Tenable (318744) and CERT Bund (WID-SEC-2026-1774). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Affected

  • Open Source X.Org X11
  • Open Source Xwayland

Productinfo

Type

Vendor

Name

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.8
VulDB Meta Temp Score: 7.8

VulDB Base Score: 7.8
VulDB Temp Score: 7.8
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 7.8
CNA Vector (redhat): 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Use after free
CWE: CWE-416 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: No

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 318744
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2026-50261

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: no mitigation known
Status: 🔍

0-Day Time: 🔒

Timelineinfo

06/04/2026 CVE reserved
06/05/2026 +1 days Advisory disclosed
06/05/2026 +0 days VulDB entry created
06/06/2026 +1 days VulDB entry last update

Sourcesinfo

Vendor: x.org

Advisory: access.redhat.com
Status: Not defined

CVE: CVE-2026-50261 (🔒)
GCVE (CVE): GCVE-0-2026-50261
GCVE (VulDB): GCVE-100-368917
CERT Bund: WID-SEC-2026-1774 - X.Org X11 und Xwayland: Mehrere Schwachstellen

Entryinfo

Created: 06/05/2026 14:06
Updated: 06/06/2026 03:43
Changes: 06/05/2026 14:06 (62), 06/05/2026 17:52 (2), 06/06/2026 03:43 (7)
Complete: 🔍
Cache ID: 216::103

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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