CVE-2026-86435 commonmark 1.5.0 before 2.8.4 Denial of Service via Footnote
Attackers can cause denial of service in commonmark by crafting documents with duplicate footnotes, leading to resource exhaustion.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-86435?
CVE-2026-86435 is a high-severity denial of service vulnerability in thephpleague commonmark, published on 7 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
commonmark versions from 1.5.0 before 2.8.4 contain a denial of service vulnerability in the Footnote extension that fails to deduplicate footnote definitions. Attackers can craft documents with duplicate footnote definitions and references to create quadratic output expansion, consuming excessive memory and CPU to exhaust server resources.
Weakness: CWE-407
Which versions are affected by CVE-2026-86435?
How do I fix CVE-2026-86435?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-86435 being exploited?
There is no known exploitation of CVE-2026-86435 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-86435, GHSA-2cmp-7fm4-4v9w, UBUNTU-CVE-2026-86435.