CVE-2026-71488 league/commonmark: Quadratic-time denial of service when parsing crafted Markdown
Attackers can cause excessive CPU consumption via crafted Markdown input in the league/commonmark PHP library, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-71488?
CVE-2026-71488 is a high-severity denial of service vulnerability in thephpleague commonmark, published on 6 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 0.6.0 until 2.9.0, specially crafted Markdown lines can cause the parser to have quadratic time complexity when converting, because several parsing paths repeatedly rescan growing portions of a line to translate between character positions and byte positions, and the Autolink extension can also copy and validate the remaining line at every URL-like prefix, allowing an attacker who can submit Markdown for conversion to consume disproportionate CPU time with a comparatively small request. This issue is fixed in 2.9.0.
Which versions are affected by CVE-2026-71488?
2 open source packages ship an affected version, including league/commonmark.
| Package | Affected | Fixed in |
|---|---|---|
league/commonmark Packagist | From 0.6.0 | 2.9.0 |
league/commonmark Packagist | From 0.6.0 | 2.9.0 |
How do I fix CVE-2026-71488?
Upgrade league/commonmark to 2.9.0 or later.
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-2026-71488 being exploited?
There is no known exploitation of CVE-2026-71488 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-71488, GHSA-2q4p-g7hv-5rgv, UBUNTU-CVE-2026-71488.