CVE-2026-56390

Arbitrary file overwrite via grammar output directives

Published Jul 29, 2026 · Updated Jul 29, 2026

External path control in GNU Bison 3.8.2 allows local users to overwrite writable files by supplying a crafted grammar. The %output and %header directives accept unrestricted file paths from the grammar and take precedence over output locations selected by the caller. Exploitation requires another user or automated workflow to process the attacker-supplied grammar, and writes remain limited to locations available to the Bison process.

CVSS severity4.6
Medium
EPSS probability0.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

External path control in GNU Bison 3.8.2 allows local users to overwrite writable files by supplying a crafted grammar. The %output and %header directives accept unrestricted file paths from the grammar and take precedence over output locations selected by the caller. Exploitation requires another user or automated workflow to process the attacker-supplied grammar, and writes remain limited to locations available to the Bison process.

The record

CVE
CVE-2026-56390
Published
Jul 29, 2026
Updated
Jul 29, 2026
Vendor
The GnuPG Project
Product
GNU Bison
Classifications
CWE-73, T1565.001
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 29, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 29, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=3.8.2

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The GnuPG Project · GNU Bisonversion=3.8.2

Published CVSS scores

6.3NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:N/I:H/A:N
4.6CERT.PLCVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-73External Control of File Name or Path
T1565.001Stored Data Manipulation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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