Read the docs
TI-2026-36755 Aliases CVE-2026-49851GHSA-qcq2-496w-v96p

Mistune: Potential DoS via quadratic-time parsing in parse_link_text

Priority HIGH 77CWE-400Published · 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: 1 fixed, 1 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-400.

Summary

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.0052 44th percentileScored 2026-11-07
Fix Partial mistune (lepture): 3.3.0mistune (PyPI): 3.3.0Red Hat: 1 advisoryRed Hat: 1 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
lepturemistunebefore 3.3.03.3.0Patch availableCNA
—mistune (PyPI)before 3.3.03.3.0Patch availableGHSA-qcq2-496w-v96p
  • mistune Vendorlepture Affected before 3.3.0 Fixed in 3.3.0 Patch available CNA
  • mistune (PyPI) Vendor— Affected before 3.3.0 Fixed in 3.3.0 Patch available GHSA-qcq2-496w-v96p

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 · CNA mistune (lepture) Fixed in 3.3.0
  • Fix · GHSA-qcq2-496w-v96p mistune (PyPI) Fixed in 3.3.0 Advisory →

Red Hat 1 advisory

  • 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

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 OpenShift AI 3.4Fixed RHSA-2026:60520
Not affected: 5 products
  • Migration Toolkit for Applications 8
  • Red Hat OpenShift AI (RHOAI)
  • Red Hat OpenShift AI 3.4
  • Red Hat OpenShift Container Platform 4
  • Red Hat Satellite 6

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-49851
  2. 2026-10-03 Alias added: GHSA-qcq2-496w-v96p

References

Advisory 1

Other 5

  • TI-2026-79440 Path traversal in Mistune include directive lets attackers read files CVSS 4.0CRITICAL 9.2
  • TI-2026-25521 Mistune ReDoS in LINK_TITLE_RE allows denial of service with crafted Markdown titles 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