Is This vulnerability exploited in the wild?

No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

How severe is This vulnerability?

High severity, with a CVSS score of 7.5, published 6 August 2026.

Which products and versions are affected?

league/commonmark (Packagist) >= 1.5.0, < 2.9.0.

Is there a fix for This vulnerability?

A patch was published on 2026-08-06: Version 2.9.0 released with fix. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is This vulnerability attacked?

It is attacked over the network, in a software library.

Check whether you run league/commonmark (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

league/commonmark denial of service in AttributesExtension

Q: Is there a fix for This vulnerability?

A patch was published on 2026-08-06: Version 2.9.0 released with fix. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is This vulnerability attacked?

It is attacked over the network, in a software library.

Q: Am I affected?

Check whether you run league/commonmark (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Severity: high · CVSS 7.5 · Published 2026-08-06

A vulnerability in the league/commonmark PHP library can allow an attacker to crash or slow down a website by submitting specially crafted text. The issue occurs when the optional Attributes extension is enabled, allowing a small amount of input to consume excessive server processing power. This can lead to a denial of service, making the affected application unavailable to legitimate users.

Technologies: league/commonmark (Packagist). Vendors: Packagist.

Quick answers

Is This vulnerability exploited in the wild?: No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
How severe is This vulnerability?: High severity, with a CVSS score of 7.5, published 6 August 2026.
Which products and versions are affected?: league/commonmark (Packagist) >= 1.5.0, < 2.9.0.
Is there a fix for This vulnerability?: A patch was published on 2026-08-06: Version 2.9.0 released with fix. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is This vulnerability attacked?: It is attacked over the network, in a software library.
Am I affected?: Check whether you run league/commonmark (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

An algorithmic complexity vulnerability (CWE-407) exists in the league/commonmark Attributes extension. The `AttributesListener::findTargetAndDirection()` function resolves attribute node targets by walking through siblings in a way that results in quadratic time complexity (O(N²)) when processing many adjacent inline attribute blocks. An unauthenticated remote attacker can exploit this by submitting a relatively small payload (e.g., 32 KB) to trigger high CPU usage and a denial of service. The vulnerability is present in all versions from 1.5.0 up to 2.9.0 when the AttributesExtension is enabled. A fix is available in version 2.9.0.

Affected products

league commonmark >= 1.5.0, < 2.9.0

Timeline

2026-08-03: disclosed: Vulnerability published to thephpleague/commonmark repository.
2026-08-06: advisory: GitHub Advisory published.
2026-08-06: patched: Version 2.9.0 released with fix.

References

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