league/commonmark's quadratic complexity bugs may lead to a denial of service
Impact
Several polynomial time complexity issues in league/commonmark may lead to unbounded resource exhaustion and subsequent denial of service.
Malicious users could trigger that inefficient code with carefully crafted Markdown inputs that are specifically designed to ensure the worst-case performance is reached. Sending multiple such requests in parallel could tie up all available CPU resources and/or PHP-FPM processes, leading to denial of service for legitimate users.
Patches
These vulnerabilities have been patched in version 2.6.0. All users on older versions are highly encouraged to upgrade as soon as possible.
Workarounds
If you cannot upgrade, you may be able to mitigate the issues by:
- Setting very low
memory_limitandmax_execution_timePHP configurations to prevent runaway resource usage - Implementing rate-limiting, bot protection, or other approaches to reduce the risk of simultaneous bad requests hitting your site
- Limiting the size of inputs fed into this library (specifically the max length of each line)
- Limiting the use of this library to trusted users
References
Most of these issues were discovered in other Markdown parsers. You can read more about them here:
- https://github.com/commonmark/commonmark.js/issues/129
- https://github.com/commonmark/commonmark.js/issues/157
- https://github.com/commonmark/commonmark.js/issues/172
- https://github.com/github/cmark-gfm/security/advisories/GHSA-r572-jvj2-3m8p
- https://github.com/github/cmark-gfm/security/advisories/GHSA-24f7-9frr-5h2r
- https://github.com/github/cmark-gfm/security/advisories/GHSA-29g3-96g3-jg6c
- https://github.com/github/cmark-gfm/security/advisories/GHSA-r8vr-c48j-fcc5
- https://github.com/github/cmark-gfm/security/advisories/GHSA-w4qg-3vf7-m9x5
- https://github.com/github/cmark-gfm/security/advisories/GHSA-66g8-4hjf-77xh
For general information about this type of issue:
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | league/commonmark | < 2.6.0 | 2.6.0 |
References
- https://github.com/github/cmark-gfm/security/advisories/GHSA-24f7-9frr-5h2r
- https://github.com/github/cmark-gfm/security/advisories/GHSA-29g3-96g3-jg6c
- https://github.com/github/cmark-gfm/security/advisories/GHSA-66g8-4hjf-77xh
- https://github.com/github/cmark-gfm/security/advisories/GHSA-r572-jvj2-3m8p
- https://github.com/github/cmark-gfm/security/advisories/GHSA-r8vr-c48j-fcc5
- https://github.com/github/cmark-gfm/security/advisories/GHSA-w4qg-3vf7-m9x5
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-c2pc-g5qf-rfrf
- https://github.com/commonmark/commonmark.js/issues/129
- https://github.com/commonmark/commonmark.js/issues/157
- https://github.com/commonmark/commonmark.js/issues/172
- https://github.com/thephpleague/commonmark
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-407- Platform
- Composer
- Package
league/commonmark- Disclosed
- 09.12.2024
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-c2pc-g5qf-rfrf - CC BY 4.0
Vulnerability history: league/commonmark
All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 18
- First → latest
- 09.2019 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 10
- Medium 8
Disclosures per year
- 2019: 1
- 2020: 0
- 2021: 0
- 2022: 1
- 2023: 0
- 2024: 1
- 2025: 1
- 2026: 14
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league/commonmark's quadratic complexity bugs may lead to a denial of service this entry
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