Red Hat Enterprise Linux 6/7/8/9 X.org X11 Server/TigerVNC XkbVModMaskText stack-based overflow

Summaryinfo

A vulnerability, which was classified as critical, has been found in Red Hat Enterprise Linux 6/7/8/9. This affects the function XkbVModMaskText of the component X.org X11 Server/TigerVNC. This manipulation causes stack-based overflow. This vulnerability is registered as CVE-2025-26595. The attack needs to be launched locally. No exploit is available.

Detailsinfo

A vulnerability has been found in Red Hat Enterprise Linux 6/7/8/9 and classified as critical. Affected by this vulnerability is the function XkbVModMaskText of the component X.org X11 Server/TigerVNC. The manipulation with an unknown input leads to a stack-based overflow vulnerability. The CWE definition for the vulnerability is 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). As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

A buffer overflow flaw was found in X.Org and Xwayland. The code in XkbVModMaskText() allocates a fixed-sized buffer on the stack and copies the names of the virtual modifiers to that buffer. The code fails to check the bounds of the buffer and would copy the data regardless of the size.

It is possible to read the advisory at access.redhat.com. This vulnerability is known as CVE-2025-26595 since 02/12/2025. The exploitation appears to be easy. Attacking locally is a requirement. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 06/06/2026).

The vulnerability scanner Nessus provides a plugin with the ID 216902 (SUSE SLED15 / SLES15 / openSUSE 15 Security Update : xorg-x11-server (SUSE-SU-2025:0730-1)), 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 (216902), EUVD (EUVD-2025-5372) and CERT Bund (WID-SEC-2025-0435). Be aware that VulDB is the high quality source for vulnerability data.

Affected

• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Fedora Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• Gentoo Linux
• IGEL OS
• SUSE openSUSE
• RESF Rocky Linux
• OpenBSD OpenBSD
• Dell NetWorker
• Dell Avamar
• Open Source X.Org X11
• Open Source Xming
• Dell PowerProtect Data Domain

Productinfo

Type

• Operating System

Vendor

• Red Hat

Name

• Enterprise Linux

Version

• 6
• 7
• 8
• 9

License

• commercial

Website

• Vendor: https://www.redhat.com/

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Be aware that VulDB is the high quality source for vulnerability data.

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