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 a denial-of-service vulnerability in Mistune versions before 3.3.0. The vulnerability arises from the parse_link_text function, which uses a regex search inside a loop that repeatedly rescans large portions of the input string when parsing Markdown with many consecutive '[' characters. This leads to quadratic-time complexity and uncontrolled CPU consumption. An attacker can exploit this by supplying crafted Markdown input to trigger excessive CPU usage. The vulnerability is resolved in Mistune 3.3.0.
Potential Impact
The vulnerability allows an unauthenticated attacker to cause a denial-of-service condition by exhausting CPU resources on systems processing malicious Markdown inputs with many consecutive '[' characters. This can degrade service availability or cause application crashes due to resource exhaustion. There are no known exploits in the wild at this time.
Mitigation Recommendations
A fix is available in Mistune version 3.3.0. Users should upgrade to version 3.3.0 or later to remediate this vulnerability. Patch status is confirmed by the vendor advisory. No additional mitigation steps 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 a denial-of-service vulnerability in Mistune versions before 3.3.0. The vulnerability arises from the parse_link_text function, which uses a regex search inside a loop that repeatedly rescans large portions of the input string when parsing Markdown with many consecutive '[' characters. This leads to quadratic-time complexity and uncontrolled CPU consumption. An attacker can exploit this by supplying crafted Markdown input to trigger excessive CPU usage. The vulnerability is resolved in Mistune 3.3.0.
Potential Impact
The vulnerability allows an unauthenticated attacker to cause a denial-of-service condition by exhausting CPU resources on systems processing malicious Markdown inputs with many consecutive '[' characters. This can degrade service availability or cause application crashes due to resource exhaustion. There are no known exploits in the wild at this time.
Mitigation Recommendations
A fix is available in Mistune version 3.3.0. Users should upgrade to version 3.3.0 or later to remediate this vulnerability. Patch status is confirmed by the vendor advisory. No additional mitigation steps 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
- Vendor Advisory Urls
- [{"url":"https://access.redhat.com/security/cve/CVE-2026-49851","vendor":"Red Hat"}]
Threat ID: 6a3c19c6eed863c81e395159
Added to database: 06/24/2026, 17:54:14 UTC
Last enriched: 07/17/2026, 08:59:52 UTC
Last updated: 08/08/2026, 00:41:14 UTC
Views: 62
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