EUVD-2026-42330Severity by source
AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
Network vector for remote content submission, no privileges if anonymous posting allowed, user interaction required to trigger anchor navigation, integrity-only impact limited to same-page navigation.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
Lifecycle Timeline
2DescriptionCVE.org
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the toc plugin and TableOfContents directive generate heading IDs as predictable toc_N values without slugifying the heading text, allowing attacker-controlled id="toc_N" content to collide with generated anchors and redirect same-page navigation, CSS selectors, or JavaScript handlers. This issue is fixed in version 3.3.0.
AnalysisAI
Predictable heading anchor ID generation in Mistune's toc plugin (all versions prior to 3.3.0) enables same-page navigation hijacking when untrusted Markdown content is rendered. The library assigns sequential numeric identifiers (toc_0, toc_1, etc.) to headings without incorporating heading text, so any party able to inject raw HTML containing a matching id attribute can pre-empt the generated anchor and redirect table-of-contents link targets, CSS selectors, or JavaScript DOM event handlers. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Three specific conditions must all be met: (1) The application must use Mistune's toc plugin or TableOfContents directive - applications using Mistune for basic Markdown rendering without this plugin are not affected. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 base score of 4.3 (AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N) appropriately characterizes this as a moderate-severity integrity issue. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker submitting Markdown content to a web application that renders it with Mistune's toc plugin enabled includes a raw HTML element such as `<span id='toc_0'>malicious anchor</span>` early in the document body. When a legitimate heading is processed, Mistune assigns it id='toc_0', but the browser resolves TOC link clicks to the earlier injected element instead, redirecting users to an unexpected page location or triggering a JavaScript handler bound to that selector. … |
| Remediation | Upgrade to Mistune 3.3.0, which fixes the predictable ID generation by incorporating heading content into anchor slug derivation. … Detailed patch versions, workarounds, and compensating controls in full report. |
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