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Fencer Vulns
high 8.6

CVE-2026-56389 json

Arbitrary Command Execution in GNU Bison

published 2026-07-29 3 mo ago modified 2026-10-23 16 d ago also EUVD-2026-50276 , GHSA-735p-4prj-f62v , JLSEC-2026-1345

cvss
8.6
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 5%
public exploits
0
none known

Summary

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.

Patch / fix

  • bison Ubuntu 22.04 LTS 2:3.8.2+dfsg-1ubuntu0.22.04.1
  • bison Ubuntu 24.04 LTS 2:3.8.2+dfsg-1ubuntu0.24.04.1
  • bison Ubuntu 26.04 LTS 2:3.8.2+dfsg-1ubuntu0.26.04.1

ubuntu advisories UBUNTU-CVE-2026-56389

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • bison Azure Linux 3.0 3.8.2-2

azure linux advisories AZL-94133

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-56389 updated cvss 5.5

bison: GNU Bison: Arbitrary Code Execution via malicious grammar file

  • Red Hat Enterprise Linux 6 bison-runtime, bison 3.8.2-9.el10
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 bison-runtime, bison 3.8.2-9.el10 Red Hat Enterprise Linux 8 bison-runtime, bison 3.8.2-9.el10 Red Hat Enterprise Linux 9 bison-runtime, bison 3.8.2-9.el10 Red Hat Enterprise Linux 10 bison 3.8.2-9.el10 Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
3 mo ago

Exploit prediction

0.16% chance of exploitation in the next 30 days, higher than 5% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 6.8 CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:L/SC:L/SI:L/SA:L
CNA 4.0 6.8 CVSS:4.0/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
NVD 3.1 8.6 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
julia Bison_jll
all versions
 no fix listed

Affected products

  • GNU Bison

Classification

Weakness
  • CWE-78 Improper Neutralization of Special Elements used in an OS Command

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.