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TI-2026-25521 Aliases CVE-2026-33079GHSA-8mp2-v27r-99xp

Mistune ReDoS in LINK_TITLE_RE allows denial of service with crafted Markdown titles

Priority HIGH 77CWE-1333Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Partial Red Hat: 2 fixed, 1 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-1333.

Summary

In versions 3.0.0a1 through 3.2.0 of Mistune, there is a ReDoS (Regular Expression Denial of Service) vulnerability in `LINK_TITLE_RE` that allows an attacker who can supply Markdown for parsing to cause denial of service. The regular expression used for parsing link titles contains overlapping alternatives that can trigger catastrophic backtracking. In both the double-quoted and single-quoted branches, a backslash followed by punctuation can be matched either as an escaped punctuation sequence or as two ordinary characters, creating an ambiguous pattern inside a repeated group. If an attacker supplies Markdown containing repeated ! sequences with no closing quote, the regex engine explores an exponential number of backtracking paths. This is reachable through normal Markdown parsing of inline links and block link reference definitions. A small crafted input can therefore cause significant CPU consumption and make applications using Mistune unresponsive.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00592 48th percentileScored 2026-11-07
Fix Partial mistune (PyPI): 3.2.1Red Hat: 2 advisoriesRed Hat: 2 fixed, 1 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
lepturemistune3.0.0a1 – 3.2.0—No fix listedCNA
—mistune (PyPI)3.0.0a1 to before 3.2.13.2.1Patch availableGHSA-8mp2-v27r-99xp
  • mistune Vendorlepture Affected 3.0.0a1 – 3.2.0 Fixed in — No fix listed CNA
  • mistune (PyPI) Vendor— Affected 3.0.0a1 to before 3.2.1 Fixed in 3.2.1 Patch available GHSA-8mp2-v27r-99xp

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*——lepture
  • cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:* Versions — — ·lepture

Remediation

  • Fix · GHSA-8mp2-v27r-99xp mistune (PyPI) Fixed in 3.2.1 Advisory →

Red Hat 2 advisories

  • RHSA-2026:60520 Released 2026-08-27 · Red Hat rating Critical
    RHOAI 3.4.4 - Red Hat OpenShift AI
    • Red Hat OpenShift AI 3.4 registry.redhat.io/rhoai/odh-automl-rhel9, registry.redhat.io/rhoai/odh-autorag-rhel9, registry.redhat.io/rhoai/odh-built-in-detector-rhel9 +47
  • RHSA-2026:43038 Released 2026-07-21 · Red Hat rating Critical
    Migration Toolkit for Applications
    • Red Hat Migration Toolkit for Applications 8.2 registry.redhat.io/mta/mta-cli-rhel9, registry.redhat.io/mta/mta-solution-server-rhel9

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat OpenShift AI (RHOAI)AffectedNo fix yet
Red Hat Migration Toolkit for Applications 8.2Fixed RHSA-2026:43038
Red Hat OpenShift AI 3.4Fixed RHSA-2026:60520
Not affected: 4 products
  • Red Hat Migration Toolkit for Applications 8.2
  • Red Hat OpenShift AI (RHOAI)
  • Red Hat OpenShift AI 3.4
  • Red Hat Satellite 6

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-33079
  2. 2026-10-03 Alias added: GHSA-8mp2-v27r-99xp
  3. 2026-10-25 EPSS moved to the below the 50th percentile

References

Advisory 1

Other 3

  • TI-2026-79440 Path traversal in Mistune include directive lets attackers read files CVSS 4.0CRITICAL 9.2
  • TI-2026-36755 Mistune: Potential DoS via quadratic-time parsing in parse_link_text CVSS 4.0HIGH 8.7
  • TI-2026-53257 Mistune has Denial of Service — RecursionError via Excessive Emphasis Markers in Markdown CVSS 3.1HIGH 7.5
  • TI-2026-42736 Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions CVSS 3.1HIGH 7.5
  • TI-2026-42730 Regular expression denial of service in lepture mistune CVSS 3.1HIGH 7.5
  • TI-2026-84319 Quadratic-time denial of service in Mistune emphasis processing CVSS 4.0HIGH 8.7
See all 30 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences