CVE-2026-49851 Details
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.
A denial-of-service vulnerability has been identified in Mistune, a Python Markdown parser, prior to version 3.3.0. The issue arises from superlinear (approximately O(n²)) behavior in the 'parse_link_text' function. When processing Markdown with many consecutive '[' characters, the function repeatedly scans the input using a regex search in a loop. This results in excessive CPU usage, as a small payload can trigger significant parsing delays. The vulnerability is rooted in a two-loop interaction that causes the parsing time to grow quadratically with the input size.
Users are advised to upgrade to Mistune version 3.3.0 or later, where this vulnerability has been fixed.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Jun 24, 2026CISA-ADP
Assessed Jun 25, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://access.redhat.com/errata/RHSA-2026:60520 | redhat-SADP | |
| https://access.redhat.com/security/cve/CVE-2026-49851 | redhat-SADP | |
| https://bugzilla.redhat.com/show_bug.cgi?id=2492304 | redhat-SADP | |
| https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-49851.json | redhat-SADP | |
| https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p | CISA-ADP | AdvisoryExploitRemedyVendor |
| https://github.com/lepture/mistune/security/advisories/GHSA-qcq2-496w-v96p | [email protected] | AdvisoryExploitRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-1333 | Inefficient Regular Expression Complexity | redhat-SADP |
| CWE-400 | Uncontrolled Resource Consumption | [email protected] |
| CWE-407 | Inefficient Algorithmic Complexity | [email protected] |
| CWE-770 | Allocation of Resources Without Limits or Throttling | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| Mistune | 3.2.1 (semver) |
CPE
Remediation
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Change History
7 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Aug 28, 2026 | CVE Modified | [email protected] |
| Aug 28, 2026 | CVE Modified | redhat-SADP |
| Aug 28, 2026 | CVE Modified | CISA-ADP |
| Jul 15, 2026 | CVE Modified | redhat-SADP |
| Jun 30, 2026 | CVE Modified | redhat-SADP |
| Jun 25, 2026 | CVE Modified | CISA-ADP |
| Jun 24, 2026 | New CVE Received | [email protected] |