Navigation hijacking via predictable heading identifier collisions
Published Jul 8, 2026 · Updated Jul 8, 2026
Identifier collision in Mistune before 3.3.0 allows remote attackers to redirect rendered-page navigation through crafted Markdown. The toc plugin and TableOfContents directive derive every default heading ID solely from its position as toc_N without checking IDs already present in attacker-controlled HTML. Exploitation requires default TOC ID generation plus a path that preserves an injected id attribute, after which a user interaction can redirect same-page links or bind CSS and JavaScript selectors to attacker-chosen content.
Summary
What happened
Identifier collision in Mistune before 3.3.0 allows remote attackers to redirect rendered-page navigation through crafted Markdown. The toc plugin and TableOfContents directive derive every default heading ID solely from its position as toc_N without checking IDs already present in attacker-controlled HTML. Exploitation requires default TOC ID generation plus a path that preserves an injected id attribute, after which a user interaction can redirect same-page links or bind CSS and JavaScript selectors to attacker-chosen content.
The record
- CVE
- CVE-2026-59930
- Published
- Jul 8, 2026
- Updated
- Jul 8, 2026
- Vendor
- Lepture
- Product
- Mistune
- Classifications
- CWE-1284, CWE-345
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 8, 2026CVE publishedPublication date reported by the CVE source.
- Jul 8, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 3.3.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Mistune TOC identifier-collision proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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