CVE-2026-59927
Description
A flaw was found in Mistune, a Python Markdown parser. The Include directive in Mistune's src/mistune/directives/include.py does not properly detect indirect cycles when two Markdown files include each other. This oversight allows for unbounded recursion, which can lead to a RecursionError and crash the rendering request, resulting in a Denial of Service (DoS) for the application using the parser.
Statement
This flaw in the Mistune Include directive can cause a denial of service when an application explicitly enables the Include plugin and renders user-controlled Markdown files from disk. Exploitation requires an attacker to place at least two coordinated Markdown files on the include search path; default Mistune configurations that parse inline strings without the Include plugin are not affected.
Mitigation
To mitigate this issue, Red Hat recommends avoiding the processing of untrusted Markdown content that may contain recursively linked include directives. Users should ensure that any Markdown files processed by applications utilizing Mistune are from trusted sources or are thoroughly sanitized to prevent indirect cyclic inclusions.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.3 | N/A | 5.3 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | Low | N/A | Low |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Amplification
An infinite loop will cause unexpected consumption of resources, such as CPU cycles or memory. The software's operation may slow down, or cause a long time to respond.
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