Is CVE-2026-86428 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-86428 being exploited in the wild.

How severe is CVE-2026-86428?

High severity, with a CVSS score of 7.5, published 7 September 2026.

Which products and versions are affected?

league/commonmark (Packagist) ECOSYSTEM:introduced=1.5.0,fixed=2.10.0.

Is there a fix for CVE-2026-86428?

Yes. league/commonmark (Packagist): upgrade to 2.10.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-86428 attacked?

It is attacked over the network.

Am I affected by CVE-2026-86428?

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.

CVE-2026-86428: commonmark denial of service in AttributesExtension

CVE-2026-86428 · Severity: high · CVSS 7.5 · Published 2026-09-07

commonmark is a Markdown parser library used to convert Markdown documents into HTML. The AttributesExtension component has a denial-of-service flaw where attackers can submit specially crafted Markdown with many distinct attribute names to trigger inefficient attribute processing that consumes excessive CPU resources, causing service slowdowns and preventing legitimate requests from completing.

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

Quick answers

Is CVE-2026-86428 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-86428 being exploited in the wild.
How severe is CVE-2026-86428?: High severity, with a CVSS score of 7.5, published 7 September 2026.
Which products and versions are affected?: league/commonmark (Packagist) ECOSYSTEM:introduced=1.5.0,fixed=2.10.0.
Is there a fix for CVE-2026-86428?: Yes. league/commonmark (Packagist): upgrade to 2.10.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-86428 attacked?: It is attacked over the network.
Am I affected by CVE-2026-86428?: 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.

How to fix

league/commonmark (Packagist): upgrade to 2.10.0 or later
```
composer require league/commonmark:^2.10.0
```

Technical details

The vulnerability is an inefficient algorithmic complexity flaw (CWE-407) in the AttributesExtension component. Two code paths exhibit quadratic time complexity (O(n²)) when processing attributes: (1) AttributesListener::processDocument() merges and filters attributes using full set traversal for each node, and (2) AttributesBlockContinueParser::tryContinue() rebuilds the entire accumulated attribute set on each continuation line. Attackers can submit untrusted Markdown with numerous distinct attribute names (via inline attributes like {a0="v"}{a1="v"}... or consecutive attribute blocks) to trigger this quadratic behavior with minimal input. No privileges, authentication, or user interaction is required; the attack is remotely exploitable via network. The AttributesExtension must be explicitly registered by the application to be vulnerable; default converters are not affected. Affected versions range from 1.5.0 to 2.9.2, with patches available in version 2.10.0 and later.

Affected products

PHP League commonmark 1.5.0 to 2.9.2

Identifiers

CVE-2026-86428
GHSA-8rr7-cvq3-gmfh

Timeline

2026-08-11: disclosed
2026-09-07: advisory
2026-09-07: patched: version 2.10.0

References

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