RCE in GNU Bison
CVE-2026-56389
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.
Vulnerability class: Command Injection (OS Command Injection)
EPSS: 0.002 (5.3th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 8.6 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H.
Affected products
- Gnu Bison — versions 3.8.2
Weakness classification (CWE)
References
- cvd@cert.pl (Third Party Advisory, third-party-advisory)
- cvd@cert.pl (Product, product)
- cvd@cert.pl (Patch, patch)
Frequently asked questions
- What is CVE-2026-56389?
- CVE-2026-56389 is a high-severity vulnerability in GNU Bison, classified under OS Command Injection. CVSS score: 8.6/10. Published 2026-07-29.
- How severe is CVE-2026-56389?
- High severity. CVSS v3 base score is 8.6 out of 10.