Summary
Mistune: Path Traversal and XSS in Include directive
The Include directive in src/mistune/directives/include.py does not validate that the resolved file path stays within the source directory, allowing path traversal via ../ sequences to read arbitrary files.
Additionally, error messages and included file contents are rendered without HTML escaping, leading to XSS even when escape=True.
Affected functions:
- Path resolution (lines 27-31)
block_error()in html.py (line 140)render_html_include()(line 72)
The Include plugin must be explicitly enabled via the plugins parameter.
Impact
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-115355? CVE-2026-115355 is a high-severity path traversal vulnerability in mistune (pip), affecting versions <= 3.2.0. It is fixed in 3.3.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- Which versions of mistune are affected by CVE-2026-115355? mistune (pip) versions <= 3.2.0 is affected.
- Is there a fix for CVE-2026-115355? Yes. CVE-2026-115355 is fixed in 3.3.0. Upgrade to this version or later.
- Is CVE-2026-115355 exploitable, and should I be worried? Whether CVE-2026-115355 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-115355 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-115355? Upgrade
mistuneto 3.3.0 or later.