CVE-2026-59924 in Mistune
Summary
by MITRE • 07/08/2026
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Include.parse() joins and normalizes user-supplied include paths without verifying that the result remains within the intended markdown directory, allowing crafted include paths to access files outside that directory when markdown files are processed using md.read(). This issue is fixed in version 3.3.0.
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Analysis
by VulDB Data Team • 07/08/2026
The Mistune Python Markdown parser vulnerability represents a critical path traversal flaw that enables unauthorized file access through improper input validation in the Include.parse() method. This vulnerability affects versions prior to 3.3.0 and specifically targets the processing of markdown files that contain include directives. When users provide markdown content with include paths, the parser performs path joining operations without adequate sanitization or directory boundary checks, creating a scenario where maliciously crafted paths can escape the intended directory context.
The technical implementation of this flaw occurs within the Include.parse() function where user-supplied paths undergo normalization and concatenation processes that do not validate whether the resulting absolute path remains within the designated markdown processing directory. This allows adversaries to craft include directives containing sequences like "../" that, when processed by md.read(), can traverse up the directory hierarchy and access files outside the intended scope. The vulnerability leverages the fundamental principle of path traversal attacks where relative path components are exploited to gain access to restricted file systems.
From an operational perspective, this vulnerability poses significant risks to applications that process untrusted markdown content, particularly those running with elevated privileges or accessing sensitive data. Attackers could exploit this weakness to read system configuration files, database credentials, application source code, or other confidential information stored outside the intended markdown processing directory. The impact extends beyond simple information disclosure as it can enable further exploitation techniques including privilege escalation and remote code execution depending on the application's access controls and the nature of accessible files.
The vulnerability aligns with CWE-22 Path Traversal and follows patterns consistent with ATT&CK technique T1059 Command and Scripting Interpreter, specifically targeting the manipulation of file system paths through markdown processing. Organizations using Mistune versions prior to 3.3.0 should immediately implement mitigations including upgrading to the patched version, implementing strict input validation for include paths, and employing directory traversal prevention mechanisms. Additional protective measures include restricting file system access permissions for markdown processing contexts, validating all user-supplied content through whitelisting approaches, and monitoring for suspicious path patterns in application logs.
The fix implemented in version 3.3.0 addresses this vulnerability by introducing proper path validation that ensures normalized include paths remain within the intended directory boundaries before processing. This remediation follows security best practices for input sanitization and defense-in-depth principles that prevent unauthorized access to system resources through malformed path specifications. Organizations should conduct comprehensive testing of their markdown processing workflows after applying the patch to ensure compatibility while maintaining security posture against this class of traversal attacks.