Vulnerability · Published Aug 6, 2026 · Assigned by GitHub_M
CVE-2026-71488league/commonmark: Quadratic-time denial of service when parsing crafted Markdown
High 7.5
In plain English
A high-severity security flaw in commonmark from thephpleague. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 50% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | php-league-commonmark | no fix listed | DEBIAN-CVE-2026-71488 |
| Debian:13 | php-league-commonmark | no fix listed | DEBIAN-CVE-2026-71488 |
| Debian:14 | php-league-commonmark | 2.9.0-1 | DEBIAN-CVE-2026-71488 |
| Packagist | league/commonmark | 2.9.0 | GHSA-2q4p-g7hv-5rgv |
| Ubuntu:22.04:LTS | commonmark | no fix listed | UBUNTU-CVE-2026-71488 |
| Ubuntu:24.04:LTS | commonmark | no fix listed | UBUNTU-CVE-2026-71488 |
| Ubuntu:26.04:LTS | commonmark | no fix listed | UBUNTU-CVE-2026-71488 |
| Ubuntu:26.10 | commonmark | no fix listed | UBUNTU-CVE-2026-71488 |
| Ubuntu:22.04:LTS | markdown | no fix listed | UBUNTU-CVE-2026-71488 |
| Ubuntu:24.04:LTS | markdown | no fix listed | UBUNTU-CVE-2026-71488 |
| Ubuntu:26.04:LTS | markdown | no fix listed | UBUNTU-CVE-2026-71488 |
| Ubuntu:26.10 | markdown | no fix listed | UBUNTU-CVE-2026-71488 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| thephpleague | commonmark | >= 0.6.0, < 2.9.0 |
Weakness: CWE-407, CWE-1050 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-2q4p-g7hv-5rgv x_refsource_CONFIRM
- https://github.com/thephpleague/commonmark/commit/a6ef6cdc308dfa39a34239c35818e75892a0e6a8 x_refsource_MISC
- https://github.com/thephpleague/commonmark/commit/a70979ea0d7d3377bd7127536748454a922bf5eb x_refsource_MISC
- https://github.com/thephpleague/commonmark/commit/c97b02e5e652b992033b93ba5d6182f706343fc6 x_refsource_MISC
- https://github.com/thephpleague/commonmark/releases/tag/2.9.0 x_refsource_MISC