CVE-2026-86428: commonmark 1.5.0 before 2.10.0 Denial of Service via Attributes
commonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when processing distinctly-named attributes. Attackers can submit Markdown with numerous distinct attribute names to cause quadratic-time attribute merging and filtering, consuming disproportionate CPU resources and preventing legitimate requests from completing.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
commonmarkto a version that resolves this vulnerability.Fixed in 2.10.0
Event History
Frequently Asked Questions
Which deployments are exposed to this denial-of-service condition?
Deployments using commonmark versions from 1.5.0 up to, but not including, 2.10.0 are affected when the AttributesExtension processes attacker-supplied Markdown.
What does an attacker need to exploit the issue?
An attacker needs to be able to submit Markdown for processing. They can include numerous distinctly named attributes, triggering quadratic-time attribute merging and filtering without requiring privileges or user interaction.
What is the operational impact of exploitation?
Processing the crafted Markdown can consume disproportionate CPU resources. This can prevent legitimate requests from completing, resulting in a denial of service.