Inefficient Algorithmic Complexity in pymdown-extensions - #VU162827
Published: November 9, 2026
Vulnerability identifier: #VU162827
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-407
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows an unauthenticated remote attacker to degrade rendering worker availability through excessive CPU consumption.
The vulnerability exists due to quadratic-time rescanning of uninterrupted delimiter runs in pymdown-extensions when rendering untrusted Markdown with pymdownx.caret, pymdownx.tilde, or pymdownx.mark enabled. An unauthenticated remote attacker can submit a request containing tens of kilobytes of repeated delimiters to occupy a render worker for seconds without victim interaction.
Affected software
pymdown-extensions
Remediation
Install security update from vendor's website.
pymdown-extensions - update to 12.1