Arbitrary Output Location Change in GNU Bison
Key facts
- Attack vector
- Local
- Privileges required
- None
- User interaction
- Active
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- —
- Confidentiality · integrity · availability
- None · Low · None
- Fix status
- Deferred Red Hat: fix deferred
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
Remediation
No fixed version listed by the sources yet.
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 10 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 8 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 9 | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Container Platform 4 | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Container Platform 5 | Affected | No fix yet: Fix deferred |
Timeline
- 2026-10-02 Threatist record created from CVE-2026-56390
- 2026-10-03 Alias added: GHSA-3pcj-vqw8-47jm
- 2026-11-06 Affected versions changed · Red Hat
References
More GNU Bison vulnerabilities
- TI-2026-40749 Arbitrary Command Execution in GNU Bison CVSS 4.0MEDIUM 6.8
- TI-2020-14854 GNU Bison before 3.7.1 has a use-after-free in _obstack_free in lib/obstack.c (called… CVSS 3.1MEDIUM 5.5
- TI-2020-11078 GNU Bison before 3.5.4 allows attackers to cause a denial of service (application crash). CVSS 3.1MEDIUM 5.5
Sources
- CVE-2026-56390 · CVE Program
- CVE-2026-56390 · NVD
- FIRST EPSS
- GHSA-3pcj-vqw8-47jm · GitHub Advisory Database · CC BY 4.0
- CVE-2026-56390 · Red Hat security data · CC BY 4.0
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