CVE-2026-56389 Arbitrary Command Execution in GNU Bison
Attackers can execute arbitrary commands by providing a malicious grammar file to GNU Bison during HTML report generation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-56389?
CVE-2026-56389 is a medium-severity command injection vulnerability in GNU Bison, published on 29 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-78
Which versions are affected by CVE-2026-56389?
It affects 1 product.
Products include Gnu Bison.
How do I fix CVE-2026-56389?
Apply the vendor's patch.
Upgrade, and pass arguments to programs as a list instead of through a shell. More about Command injection.
Is CVE-2026-56389 being exploited?
There is no known exploitation of CVE-2026-56389 in the wild and no public exploit code.
Other vulnerabilities in GNU Bison
Sources
Also known as AZL-94133, DEBIAN-CVE-2026-56389, ECHO-5a4d-f9a3-722e, GHSA-735p-4prj-f62v, JLSEC-2026-1345, UBUNTU-CVE-2026-56389 and 1 more.