CVE-2026-56390
MediumCVSS 6.3Exploitation Probability (EPSS)
Low risk3th percentile - higher than 3% of all known CVEs
Summary
GNU Bison improperly handles grammar-defined output paths. Directives %output and %header allow arbitrary file paths, which are accepted without restriction, potentially overwriting files. Confirmed vulnerable in version 3.8.2, other versions may also be affected.
Risk Assessment
An attacker can overwrite any file accessible to the Bison process, potentially leading to privilege escalation or system compromise.
Recommendation
Update GNU Bison to the latest version containing the fix (commit 8d101c19d4d9aaedf83a448c925513742d4efcf0).
Other vulnerabilities in GNU Bison
Original NVD description (English source)
GNU Bison improperly handles grammar‑defined output paths. Grammar directives such as %output and %header allow specifying file paths, which are accepted without restriction and override caller‑supplied output options. When processing attacker-supplied grammar, this behavior allows directing generated files to arbitrary writable locations on the filesystem, potentially overwriting existing files accessible to the Bison process. Maintainers of this project were notified about this vulnerability, and fixed the issue in commit 8d101c19d4d9aaedf83a448c925513742d4efcf0. 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.