CVE-2026-56389 GNU CVE debrief

Who should care

GNU Bison users, developers, and maintainers should be aware of this vulnerability and take necessary actions to protect their systems. Affected operators should review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance. Platform administrators, vulnerability-management teams, and security teams should plan vendor-supported updates or mitigations through normal change control where exposure is confirmed. They should also review compensating controls for exposed systems while remediation is scheduled and verified, and check relevant monitoring, detection, and logs for exposed assets that need extra review. Asset inventory management and source tracking are crucial in addressing this vulnerability. Additionally, tracking exceptions, retesting remediated assets, and closing the item only after evidence is documented are essential steps in the remediation process. Users should also consider implementing monitoring and compensating controls to mitigate potential impacts. GNU Bison users should confirm whether affected product deployments exist in managed environments and assign an owner for follow-up. They should also consider rollback/change windows as part of their remediation strategy. Effective communication and coordination among these groups are vital to ensure comprehensive mitigation of the vulnerability. GNU Bison users and developers must prioritize patching or updating to the fixed version to prevent exploitation. Security teams should verify that all necessary steps are taken to secure Bison installations. By taking these measures, organizations can minimize the risk associated with CVE-2026-56389 and protect their systems from potential attacks. The CVE record was published on 2026-07-29T11:16:49.767Z and has not been modified since then. The NVD entry is currently Analyzed. 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. This vulnerability has

Technical summary

The CVE-2026-56389 vulnerability in GNU Bison allows for 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 the XML-to-HTML transformation step via %define tool.xsltproc, which is accepted without restriction and passed directly to execvp(). This behavior allows execution of an arbitrary program with the privileges of the Bison process when running bison --html on an attacker-provided grammar.

Defensive priority

Medium-priority defensive actions are required to address CVE-2026-56389, a vulnerability in GNU Bison that allows for arbitrary program execution during HTML report generation.

Recommended defensive actions

• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Implement source tracking to ensure that all affected systems are properly updated and monitored.

Evidence notes

The CVE-2026-56389 vulnerability in GNU Bison allows for 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 the XML-to-HTML transformation step via %define tool.xsltproc, which is accepted without restriction and passed directly to execvp(). Maintainers were notified and fixed the issue in commit 3169c1e7a2c6acc4c59dfcf8b089896d6881925b, but did not provide a vulnerable version range. Version 3.8.2 was tested and confirmed as vulnerable; other versions may also be vulnerable but were not tested.

Official resources