CVE-2026-49851

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.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p
https://access.redhat.com/errata/RHSA-2026:60520
https://access.redhat.com/security/cve/CVE-2026-49851
https://bugzilla.redhat.com/show_bug.cgi?id=2492304
https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json

Configurations

No configuration.

History

No history.

Information

Published : 2026-06-24 18:17

Updated : 2026-08-28 16:18

NVD link : CVE-2026-49851

Mitre link : CVE-2026-49851

CVE.ORG link : CVE-2026-49851

JSON object : View

Products Affected

No product.

CWE

CWE-400

Uncontrolled Resource Consumption

CWE-407

Inefficient Algorithmic Complexity

CWE-770

Allocation of Resources Without Limits or Throttling

CWE-1333

Inefficient Regular Expression Complexity

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renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n\u00b2)) 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."}], "lastModified": "2026-08-28T16:18:13.200", "sourceIdentifier": "security-advisories@github.com"}