Vulnerability · Published Jul 29, 2026 · Assigned by CERT-PL
CVE-2026-56389Arbitrary Command Execution in GNU Bison
Medium 6.8
In plain English
A medium-severity OS command injection in Bison from GNU. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 13% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | bison | no fix listed | DEBIAN-CVE-2026-56389 |
| Debian:13 | bison | no fix listed | DEBIAN-CVE-2026-56389 |
| Debian:14 | bison | no fix listed | DEBIAN-CVE-2026-56389 |
| Ubuntu:22.04:LTS | bison | 2:3.8.2+dfsg-1ubuntu0.22.04.1 | UBUNTU-CVE-2026-56389 |
| Ubuntu:22.04:LTS | bison | 2:3.8.2+dfsg-1ubuntu0.22.04.1 | USN-8777-1 |
| Ubuntu:24.04:LTS | bison | 2:3.8.2+dfsg-1ubuntu0.24.04.1 | USN-8777-1 |
| Ubuntu:24.04:LTS | bison | 2:3.8.2+dfsg-1ubuntu0.24.04.1 | UBUNTU-CVE-2026-56389 |
| Ubuntu:26.04:LTS | bison | 2:3.8.2+dfsg-1ubuntu0.26.04.1 | USN-8777-1 |
| Ubuntu:26.04:LTS | bison | 2:3.8.2+dfsg-1ubuntu0.26.04.1 | UBUNTU-CVE-2026-56389 |
Affected products (as reported)
Weakness: CWE-78 · Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:L/SC:L/SI:L/SA:L