Medium [CVE-2026-11979] Arbitrary code execution in xmlcatalog utility via buffer overflow

libxml2 is vulnerable to multiple stack-based buffer overflows in the xmlcatalog utility when running in --shell mode. The usershell() function processes user input using fixed-size stack buffers without proper bounds checking.

By supplying an overly long input line, an attacker can overflow internal buffers (command, arg, and argv) during input parsing. This results in memory corruption within the stack frame.

Successful exploitation may cause a crash or potentially allow arbitrary code execution in the context of the xmlcatalog process. This issue has been fixed in the commit c2e233fc.

NOTE: The maintainers of this project did not agree that this issue is a vulnerability and considered it a bug. An attacker can exploit multiple stack-based buffer overflows by providing an excessively long input line.

This vulnerability is limited to scenarios where an attacker can control input to the `xmlcatalog` utility, reducing its overall exposure in typical Red Hat deployments. Red Hat severity: Moderate — CVSS 4.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:L).

Weakness: CWE-120. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9; Red Hat Discovery 2; Red Hat Hardened Images; Red Hat Update Infrastructure 5; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat OpenShift Container Platform 4.