CVE-2026-59924: Mistune Path Traversal Vulnerability

MODERATE
Advisory Identifier: GHSA-r4rv-85jg-w4mf
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CVSS 5.9
CWE-22
Published
Advisory Summary

CVE-2026-59924 is a MODERATE (CVSS 5.9) path traversal vulnerability (CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')) affecting Mistune libraries in the PyPI ecosystem. The issue involves arbitrary file read via include directive path traversal. Remediation is available by upgrading affected packages to version 3.3.0.

CVE-2026-59924 at a Glance

CVE Identifier CVE-2026-59924
GHSA Identifier GHSA-r4rv-85jg-w4mf
Severity MODERATE
CVSS v3.1 Base Score 5.9
CWE Classification CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Affected Product Mistune
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 5.9

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2026-59924

To remediate this vulnerability, upgrade all affected Mistune dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

mistune fixed: 3.3.0 
pip install mistune>=3.3.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show mistune

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-59924, inspect your installed packages using pip:

pip show mistune

Analyze the terminal output to locate any version of Mistune in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.3.0), your application is affected.

Note: The pip show mistune command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'), where the product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. In Mistune, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Summary A path traversal issue exists in mistune's `Include` directive when markdown files are processed using `md.read()`. A crafted include path can cause files outside the intended markdown directory to be accessed. ### Details The issue occurs in the `Include.parse()` method where user-supplied paths are joined and normalized without verifying that the resulting path remains within an expected directory. ```python relpath = self.parse_title(m) dest = os.path.join(os.path.dirname(source_file), relpath) dest = os.path.normpath(dest) ``` Because the final path is not restricted to a trusted base directory, path traversal sequences such as `../` may reference files outside the intended location. ### Proof of Concept Create a markdown file: ```markdown .. include:: ../../../example.txt ``` Process it using: ```python import mistune from mistune.directives import RSTDirective, Include md = mistune.create_markdown( plugins=[RSTDirective([Include()])] ) result, state = md.read("test.md") print(result) ``` ### Impact Applications that process untrusted markdown files with the `Include` directive enabled may allow unintended file access. The impact depends on how the feature is used and what files are accessible to the running process. ### Recommended Fix Validate the resolved path and ensure it remains within an allowed directory before opening the file.

CVE-2026-59924 Affected Mistune Versions

1 component(s)
Fixed Versions:
3.3.0
Product / Package Ecosystem Affected Versions Fixed Version
mistune
pypi/mistune
PyPI
< 3.3.0
3.3.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/lepture/mistune/security/advisories/GHSA-r4rv-85jg-w4mf
NVD — CVE-2026-59924 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59924
Security Fix Commit FIX COMMIT
https://github.com/lepture/mistune/commit/1bef343ade163fc3bb95572b15be720084cdb993
Mistune Source Repository REPOSITORY
https://github.com/lepture/mistune
Mistune Release RELEASE
https://github.com/lepture/mistune/releases/tag/v3.3.0
Mistune Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/mistune/PYSEC-2026-2212.yaml

Frequently Asked Questions

What is CVE-2026-59924?
CVE-2026-59924 is a security vulnerability in Mistune involving Arbitrary File Read via Include directive path traversal under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal').
Which Mistune versions are affected?
Affected versions include releases prior to 3.3.0 across affected packages: mistune.
What version fixes CVE-2026-59924?
Upgrading to 3.3.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is mistune affected?
Yes, mistune is affected in releases prior to 3.3.0. Upgrade your dependency to 3.3.0 or later.
What is the CVSS score of CVE-2026-59924?
CVE-2026-59924 has a CVSS v3.1 base score of 5.9 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2026-59924?
CVE-2026-59924 is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') (The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.).
How can I check PyPI dependencies for CVE-2026-59924?
Run the dependency tree command: 'pip show mistune'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-r4rv-85jg-w4mf",
  "modified" : "2026-07-20T21:34:53Z",
  "published" : "2026-07-20T21:34:53Z",
  "aliases" : [ "CVE-2026-59924" ],
  "summary" : "Mistune: Arbitrary File Read via Include directive path traversal",
  "details" : "### Summary\n\nA path traversal issue exists in mistune's `Include` directive when markdown files are processed using `md.read()`. A crafted include path can cause files outside the intended markdown directory to be accessed.\n\n### Details\n\nThe issue occurs in the `Include.parse()` method where user-supplied paths are joined and normalized without verifying that the resulting path remains within an expected directory.\n\n```python\nrelpath = self.parse_title(m)\ndest = os.path.join(os.path.dirname(source_file), relpath)\ndest = os.path.normpath(dest)\n```\n\nBecause the final path is not restricted to a trusted base directory, path traversal sequences such as `../` may reference files outside the intended location.\n\n### Proof of Concept\n\nCreate a markdown file:\n\n```markdown\n.. include:: ../../../example.txt\n```\n\nProcess it using:\n\n```python\nimport mistune\nfrom mistune.directives import RSTDirective, Include\n\nmd = mistune.create_markdown(\n    plugins=[RSTDirective([Include()])]\n)\n\nresult, state = md.read(\"test.md\")\nprint(result)\n```\n\n### Impact\n\nApplications that process untrusted markdown files with the `Include` directive enabled may allow unintended file access. The impact depends on how the feature is used and what files are accessible to the running process.\n\n### Recommended Fix\n\nValidate the resolved path and ensure it remains within an allowed directory before opening the file.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "mistune"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.3.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/lepture/mistune/security/advisories/GHSA-r4rv-85jg-w4mf"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-59924"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lepture/mistune/commit/1bef343ade163fc3bb95572b15be720084cdb993"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/lepture/mistune"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lepture/mistune/releases/tag/v3.3.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/mistune/PYSEC-2026-2212.yaml"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-20T21:34:53Z",
    "nvd_published_at" : "2026-07-08T17:17:28Z"
  }
}