CVE-2026-67422
Description
A flaw was found in pymdown-extensions, a collection of extensions for the Python Markdown library. This vulnerability, known as a Regular Expression Denial of Service (ReDoS), arises from how certain inline processors handle regular expressions. An unauthenticated remote attacker can exploit this by submitting a short, untrusted Markdown line that causes the regular expression engine to perform an excessive number of calculations. This leads to unbounded CPU usage, effectively causing a denial of service for affected web applications or systems that process user-supplied Markdown.
Statement
This vulnerability is rated Important as it enables an unauthenticated remote attacker to trigger a Regular Expression Denial of Service (ReDoS) in Red Hat products that render untrusted Markdown via pymdown-extensions. Catastrophic backtracking in specific inline processors can lead to excessive CPU usage and service disruption.
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 | 7.5 | N/A | 7.5 |
| 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 | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/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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