EUVD-2026-42339Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Triggering the cycle requires writing two mutually-referencing files to the server, implying PR:L and AC:H rather than vendor's PR:N/AC:L.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Lifecycle Timeline
2DescriptionCVE.org
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the Include directive in src/mistune/directives/include.py detects only direct self-includes and not indirect cycles, allowing two markdown files that include each other to trigger unbounded recursion, raise RecursionError, and crash the rendering request. This issue is fixed in version 3.3.0.
AnalysisAI
Unbounded recursion in Mistune's Include directive (all versions prior to 3.3.0) can be triggered by a pair of mutually-referencing markdown files, bypassing the cycle detector that only checks for direct self-inclusion. An attacker who can supply markdown content processed by an application using the Include directive may crash the rendering request with a Python RecursionError, resulting in a denial of service. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The Include directive (src/mistune/directives/include.py) must be explicitly enabled and active in the target application - it is an optional Mistune feature, not enabled in all deployments. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor-assigned CVSS 5.3 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L) characterizes this as a low-complexity, unauthenticated network attack with limited availability impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker with the ability to create or upload markdown content to a Mistune-powered application constructs two files where file A contains an include reference to file B and file B contains an include reference back to file A. When any user or automated process triggers a render of either file, Mistune's Include directive recursively processes the chain without bound, exhausting the Python interpreter's call stack and raising a RecursionError that crashes the rendering request. … |
| Remediation | Upgrade Mistune to version 3.3.0, which introduces indirect cycle detection for the Include directive. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-674 – Uncontrolled Recursion
View allSame technique Denial Of Service
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External POC / Exploit Code
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