CVE-2026-56389
Arbitrary Command Execution in GNU Bison
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.
INFO
Published Date :
July 29, 2026, 11:16 a.m.
Last Modified :
Oct. 23, 2026, 11:10 p.m.
Remotely Exploit :
No
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 4.0 | MEDIUM | 4bb8329e-dd38-46c1-aafb-9bf32bcb93c6 | ||||
| CVSS 4.0 | MEDIUM | [email protected] |
Solution
- Update GNU Bison to the latest version.
- Apply the fix from commit 3169c1e7a2c6acc4c59dfcf8b089896d6881925b.
- Validate grammar file inputs for safety.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-56389.
| URL | Resource |
|---|---|
| https://cert.pl/en/posts/2026/07/CVE-2026-56389 | Third Party Advisory |
| https://cgit.git.savannah.gnu.org/cgit/bison.git/ | Product |
| https://cgit.git.savannah.gnu.org/cgit/bison.git/commit/?id=3169c1e7a2c6acc4c59dfcf8b089896d6881925b | Patch |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-56389 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-56389
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-56389 vulnerability anywhere in the article.
-
cert.pl
Vulnerabilities in GNU Bison software
Vulnerabilities in GNU Bison software CVE ID CVE-2026-56389 Publication date 29 July 2026 Vendor GNU Product Bison Vulnerable versions 3.8.2 Vulnerability type (CWE) Improper Neutralization of Special ... Read more
The following table lists the changes that have been made to the
CVE-2026-56389 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Translated by [email protected]
Oct. 23, 2026
Action Type Old Value New Value Added Translation Title: Bison de GNU, Description: GNU Bison permite la ejecución de un programa arbitrario durante la generación de informes HTML debido a un manejo inadecuado de las variables de configuración definidas por la gramática. Un archivo de gramática puede anular el ejecutable utilizado para el paso de transformación de XML a HTML a través de %define tool.xsltproc, que se acepta sin restricciones y se pasa directamente a execvp(). Al ejecutar bison --html en una gramática proporcionada por un atacante, este comportamiento permite la ejecución de un programa arbitrario con los privilegios del proceso de Bison. Los mantenedores de este proyecto fueron notificados sobre esta vulnerabilidad y corrigieron el problema en el commit 3169c1e7a2c6acc4c59dfcf8b089896d6881925b. Sin embargo, no proporcionaron el rango de versiones vulnerables. La versión 3.8.2 fue probada y confirmada como vulnerable; otras versiones no fueron probadas, pero también podrían ser vulnerables. -
Initial Analysis by [email protected]
Aug. 24, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H Added CPE Configuration OR *cpe:2.3:a:gnu:bison:3.8.2:*:*:*:*:*:*:* Added Reference Type CERT.PL: https://cert.pl/en/posts/2026/07/CVE-2026-56389 Types: Third Party Advisory Added Reference Type CERT.PL: https://cgit.git.savannah.gnu.org/cgit/bison.git/ Types: Product Added Reference Type CERT.PL: https://cgit.git.savannah.gnu.org/cgit/bison.git/commit/?id=3169c1e7a2c6acc4c59dfcf8b089896d6881925b Types: Patch -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 29, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-56389', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-29T12:20:29.904189Z'} -
New CVE Received by [email protected]
Jul. 29, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://cgit.git.savannah.gnu.org/cgit/bison.git/', 'vendor': 'GNU', 'product': 'Bison', 'versions': [{'status': 'affected', 'version': '3.8.2', 'versionType': 'semver'}], 'defaultStatus': 'unknown'}] Added 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. Added CVSS V4.0 AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:L/SC:L/SI:L/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-78 Added Reference https://cert.pl/en/posts/2026/07/CVE-2026-56389 Added Reference https://cgit.git.savannah.gnu.org/cgit/bison.git/ Added Reference https://cgit.git.savannah.gnu.org/cgit/bison.git/commit/?id=3169c1e7a2c6acc4c59dfcf8b089896d6881925b