X.org X11 Server stack-based overflow

Summaryinfo

A vulnerability was found in X.org X11 Server. It has been classified as critical. The affected element is an unknown function. The manipulation leads to stack-based overflow. This vulnerability is documented as CVE-2026-50256. The attack needs to be performed locally. There is not any exploit available.

Detailsinfo

A vulnerability was found in X.org X11 Server (unknown version). It has been rated as critical. This issue affects an unknown code block. The manipulation with an unknown input leads to a stack-based overflow vulnerability. Using CWE to declare the problem leads to CWE-121. A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function). Impacted is confidentiality, integrity, and availability. The summary by CVE is:

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. A mismatch between the X server and the libXfont2 library's maximum font name length can cause a stack buffer overflow during font alias resolution. The server allocates a 256 byte stack buffer but libXfont2's alias target name length is 1024 bytes. A font alias name between 257 and 1023 bytes causes the X server to copy that name into the undersized stack buffer without further checks. This may be used to crash the server, or for privilege escalation if the X server runs as root.

It is possible to read the advisory at access.redhat.com. The identification of this vulnerability is CVE-2026-50256 since 06/04/2026. The exploitation is known to be easy. Attacking locally is a requirement. The technical details are unknown and an exploit is not publicly available. The pricing 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 318749 (Linux Distros Unpatched Vulnerability : CVE-2026-50256), 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 (318749) and CERT Bund (WID-SEC-2026-1774). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

• Open Source X.Org X11
• Open Source Xwayland

Productinfo

Type

• Windowing System Software

Vendor

• X.org

Name

• X11 Server

License

• open-source

Website

• Vendor: https://www.x.org/

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CPE 2.2info

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Entryinfo

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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