CVE-2026-49851: CWE-400: Uncontrolled Resource Consumption in lepture mistune
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.
AI Analysis
Technical Summary
CVE-2026-49851 describes an uncontrolled resource consumption vulnerability (CWE-400) in the Mistune Markdown parser before version 3.3.0. The vulnerability arises from the parse_link_text function's superlinear (approximately O(n²)) behavior when parsing Markdown containing many consecutive '[' characters. This function repeatedly applies a regex search inside a loop, causing repeated rescanning of large portions of the input string. An attacker can exploit this by crafting a small Markdown payload that triggers excessive CPU usage, resulting in a denial-of-service condition. The vulnerability is resolved in Mistune version 3.3.0.
Potential Impact
An attacker can cause a denial-of-service by triggering excessive CPU consumption in applications using vulnerable versions of Mistune. This can degrade service availability or cause application unresponsiveness. There are no indications of privilege escalation, data disclosure, or other impacts beyond resource exhaustion.
Mitigation Recommendations
Upgrade Mistune to version 3.3.0 or later, where this vulnerability is fixed. Patch status is confirmed by the vendor stating the fix in version 3.3.0. No other mitigations are indicated.
CVE-2026-49851: CWE-400: Uncontrolled Resource Consumption in lepture mistune
Description
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 v4.0
Score 8.7high
Affected software
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-49851 describes an uncontrolled resource consumption vulnerability (CWE-400) in the Mistune Markdown parser before version 3.3.0. The vulnerability arises from the parse_link_text function's superlinear (approximately O(n²)) behavior when parsing Markdown containing many consecutive '[' characters. This function repeatedly applies a regex search inside a loop, causing repeated rescanning of large portions of the input string. An attacker can exploit this by crafting a small Markdown payload that triggers excessive CPU usage, resulting in a denial-of-service condition. The vulnerability is resolved in Mistune version 3.3.0.
Potential Impact
An attacker can cause a denial-of-service by triggering excessive CPU consumption in applications using vulnerable versions of Mistune. This can degrade service availability or cause application unresponsiveness. There are no indications of privilege escalation, data disclosure, or other impacts beyond resource exhaustion.
Mitigation Recommendations
Upgrade Mistune to version 3.3.0 or later, where this vulnerability is fixed. Patch status is confirmed by the vendor stating the fix in version 3.3.0. No other mitigations are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-01T22:03:19.640Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a3c19c6eed863c81e395159
Added to database: 06/24/2026, 17:54:14 UTC
Last enriched: 06/24/2026, 18:09:12 UTC
Last updated: 06/24/2026, 18:31:10 UTC
Views: 5
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