Arbitrary code execution in xmlcatalog utility via buffer overflow

Summary

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. A flaw was found in libxml2, specifically within the xmlcatalog utility when operating in shell mode. An attacker can exploit multiple stack-based buffer overflows by providing an excessively long input line. This leads to memory corruption, which may cause the application to crash or potentially allow the attacker to execute arbitrary code within the context of the xmlcatalog process. 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. Fixed by RHSA-2026:33840 — update the affected packages (`sudo dnf update`). Affected Red Hat products: Red Hat Hardened Images.