CVE-2026-59922
Description
A flaw was found in Mistune, a Python Markdown parser. A remote attacker could exploit this vulnerability by providing specially crafted input containing specific marker pairs (tilde, equals-sign, or caret). This crafted input causes the parser to perform quadratic work, leading to excessive CPU consumption. This can result in a denial of service (DoS) for the affected system.
Statement
This Moderate flaw in the Mistune Python Markdown parser can lead to a denial of service. When processing specially crafted markdown input with a high number of specific formatting marker pairs (such as tilde, equals-sign, or caret), the parser can consume excessive CPU resources. This vulnerability primarily affects Red Hat products where the strikethrough, mark, or insert plugins are explicitly enabled, as these are not part of Mistune's default configuration.
Mitigation
To mitigate this vulnerability, disable the `strikethrough`, `mark`, and `insert` plugins if they are not essential for your application's functionality. These plugins are not enabled by default in Mistune. Consult your application's documentation for specific instructions on how to configure or disable Mistune plugins. If the application does not explicitly enable these plugins, no further action is required.
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 | 6.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | Low | 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 | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU)
Attackers can create crafted inputs that intentionally cause the regular expression to use excessive backtracking in a way that causes the CPU consumption to spike.
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