CVE-2026-56389

HighCVSS 8.6

Published: 29/07/2026(UTC)Updated: 24/08/2026(UTC)Translated: 29/07/2026(UTC)NVD NIST

Exploitation Probability (EPSS)

Low risk

0.15%

5th percentile - higher than 5% of all known CVEs

Summary

GNU Bison allows arbitrary program execution during HTML report generation due to improper handling of grammar-defined configuration variables. A grammar file can override the executable used for XML-to-HTML transformation via %define tool.xsltproc, which is accepted without restriction and passed directly to execvp(). Running bison --html on an attacker-provided grammar enables execution of an arbitrary program with the privileges of the Bison process.

Risk Assessment

An attacker can execute arbitrary code on the server running Bison, potentially leading to system compromise or data theft.

Recommendation

Update GNU Bison to a version containing the fix from commit 3169c1e7a2c6acc4c59dfcf8b089896d6881925b or later. Avoid running bison --html on untrusted grammar files.

Other vulnerabilities in GNU Bison

CVE-2026-56390Medium
GNU Bison improperly handles grammar-defined output paths. Directives %output and %header allow arbitrary file paths, which are accepted without restriction, potentially overwriting files. Confirmed vulnerable in version 3.8.2, other versions may also be affected.

Original NVD description (English source)

GNU Bison allows for an execution of an arbitrary program during HTML report generation due to improper handling of grammar-defined configuration variables. A grammar file can override the executable used for the XML‑to‑HTML transformation step via %define tool.xsltproc, which is accepted without restriction and passed directly to execvp(). When running bison --html on a attacker-provided grammar, this behavior allows execution of an arbitrary program with the privileges of the Bison process. Maintainers of this project were notified about this vulnerability, and fixed the issue in commit 3169c1e7a2c6acc4c59dfcf8b089896d6881925b. However, they did not provide vulnerable version range. Version 3.8.2 was tested and confirmed as vulnerable, other versions were not tested but might also be vulnerable.