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Fencer Intel
high 7.5

CVE-2026-67422 json

pymdown-extensions: Exponential-backtracking ReDoS in caret, tilde, betterem, and magiclink inline processors

published 3mo ago modified 18d ago also EUVD-2026-54256 , GHSA-gm37-52c6-37mw , PYSEC-2026-3654

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 54%
public exploits
0
none known

Summary

pymdown-extensions is a collection of extensions for the Python Markdown library. In versions up to and including 11.0, four inline processors (caret, tilde, betterem, and magiclink) use regular expressions whose content groups can partition a run of delimiter characters in exponentially many ways, causing catastrophic backtracking. As a result, a single untrusted Markdown line under 50 bytes rendered with markdown.markdown() in each extension's default configuration drives the rendering thread into unbounded CPU usage that grows exponentially with input length, enabling an unauthenticated remote attacker who can submit Markdown to cause denial of service. The exposure is concrete for web applications that render user-supplied Markdown (comments, wikis, issue bodies, live preview), including any app using pymdownx.extra which bundles the vulnerable betterem default, as well as hosted docs/CI systems that build untrusted Markdown. The issue has been fixed in version 11.0.1.

Patch / fix

  • pypi pymdown-extensions 11.0.1
  • facelessuser pymdown_extensions 11.0.1
  • pymdown_extensions_project pymdown_extensions 11.0.1
  • pymdown-extensions Debian 14 11.0.1-1

debian advisories DEBIAN-CVE-2026-67422

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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-2026-67422 updated cvss 7.5

pymdown-extensions: Pymdown-extensions: Denial of Service via Regular Expression Vulnerability

  • Red Hat Ansible Automation Platform 2.2 ansible-automation-platform/bootc-automation-portal-rhel9 1788943531
    fixed: vendor fix RHSA-2026:66003
  • Red Hat Developer Hub 1.9 rhdh/rhdh-hub-rhel9 1789554285
    fixed: vendor fix RHSA-2026:69248
  • Red Hat Developer Hub 1.10 rhdh/rhdh-hub-rhel9 1791311495
    fixed: vendor fix RHSA-2026:79088
  • Red Hat Developer Hub 1.9 rhdh/rhdh-rhel9-operator 1789552931, rhdh/rhdh-operator-bundle 1789558887 Red Hat Developer Hub 1.10 rhdh/rhdh-rhel9-operator 1791219676, rhdh/rhdh-operator-bundle 1791315788, rhdh/rhdh-must-gather-rhel9 1788278523, rhdh/rhdh-rag-content-rhel9 1791168570
    not affected: vulnerable code not present
  • Red Hat Hardened Images trivy 0.73.0-0.1.hum1, grafana12.4 12.4.7-0.1.hum1, grafana13.1 13.1.2-0.1.hum1
    not affected: component not present
  • Red Hat OpenShift Container Platform 4 openshift4/ose-olm-catalogd-rhel9
    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
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
3mo ago

Exploit prediction

0.72% chance of exploitation in the next 30 days, higher than 54% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • github.com https://github.com/facelessuser/pymdown-extensions/security/advisories/GHSA-gm37-52c6-37mw referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi pymdown-extensions
<11.0.1
11.0.1

Affected products

  • facelessuser pymdown-extensions

Classification

Weakness
  • CWE-1333 Inefficient Regular Expression Complexity

References

Sources

Fencer Intel 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.

The maintainers of facelessuser/pymdown-extensions published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.