CVE-2026-49851

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.

Affected Software

Weaknesses

• CWE-400: CWE-400: Uncontrolled Resource Consumption
• CWE-770: CWE-770: Allocation of Resources Without Limits or Throttling
• CWE-407: CWE-407: Inefficient Algorithmic Complexity

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: yes
  • Technical Impact: partial

Additional References

• https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p

Mistune: Mistune: Denial of Service via crafted Markdown input

Additional References

• https://access.redhat.com/security/cve/CVE-2026-49851
• https://bugzilla.redhat.com/show_bug.cgi?id=2492304
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json

References

• https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p

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