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Fencer Vulns
medium 5.3

CVE-2026-59927 json

Mistune directives/include: mutual `.. include::` recursion crashes the renderer with `RecursionError`, denial of service via two attacker-controlled markdown files

published 2026-07-08 4 mo ago modified 2026-10-25 14 d ago also GHSA-8mpj-m6qm-5qr8 , PYSEC-2026-2215 , EUVD-2026-42339

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 45%
public exploits
0
none known

Summary

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.

Patch / fix

  • pypi mistune 3.3.0
  • mistune_project mistune 3.3.0
  • python-mistune SLES for SAP applications 16.0, SLES 16.0 3.1.3-160000.5.1

suse advisories SUSE-SU-2026:22655-1

  • python-mistune openSUSE Leap 16.0 3.1.3-160000.5.1

opensuse advisories openSUSE-SU-2026:21339-1

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-2026-59927 updated cvss 5.3

mistune: Mistune: Denial of Service via unbounded recursion in Markdown include directive

  • Red Hat Migration Toolkit for Applications 8 mta/mta-solution-server-rhel9 Red Hat OpenShift AI (RHOAI) rhoai/odh-th06-cpu-torch210-py312-rhel9, rhoai/odh-th06-cpu-torch291-py312-rhel9, rhoai/odh-th06-rocm64-torch291-py312-rhel9, rhoai/odh-th06-cuda130-torch210-py312-rhel9, rhoai/odh-th06-cuda130-torch291-py312-rhel9, rhoai/odh-pipeline-runtime-minimal-cpu-py312-rhel9, +16 more Red Hat OpenShift Container Platform 4 python-mistune 0.8.3-15.2.el9ocp Red Hat Satellite 6 satellite/iop-advisor-engine-rhel9
    affected: workaround, no fix available “Fix deferred”

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
yes
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.53% chance of exploitation in the next 30 days, higher than 45% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/lepture/mistune/security/advisories/GHSA-8mpj-m6qm-5qr8 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
GitHub 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
OSV 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected packages

ecosystem package affected fixed in
pypi mistune
<3.3.0
3.3.0

Affected products

  • lepture mistune

Classification

Weakness
  • CWE-674 Uncontrolled Recursion
  • CWE-755 Improper Handling of Exceptional Conditions

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.