Is CVE-2026-86433 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-86433 being exploited in the wild.

How severe is CVE-2026-86433?

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

Which products and versions are affected?

League CommonMark 1.5.0 before 2.8.4.

Is there a fix for CVE-2026-86433?

A patch was published on 2026-09-07. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-86433 attacked?

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

Am I affected by CVE-2026-86433?

Check whether anything you run is named in the advisory. 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-2026-86433: commonmark Attributes extension denial of service via quadratic parsing

CVE-2026-86433 · Severity: high · CVSS 7.5 · Published 2026-09-07

The League CommonMark library contains a denial-of-service vulnerability in its optional Attributes extension when processing markdown documents. An unauthenticated attacker can send a specially crafted 32 KB payload of repeated attribute blocks that causes the parser to consume excessive CPU time (over 5 seconds), degrading server performance and availability.

Quick answers

Is CVE-2026-86433 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-86433 being exploited in the wild.
How severe is CVE-2026-86433?: High severity, with a CVSS score of 7.5, published 7 September 2026.
Which products and versions are affected?: League CommonMark 1.5.0 before 2.8.4.
Is there a fix for CVE-2026-86433?: A patch was published on 2026-09-07. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-86433 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-86433?: Check whether anything you run is named in the advisory. 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

The vulnerability is an inefficient algorithmic complexity flaw (CWE-407) in the AttributesListener::findTargetAndDirection() method within the Attributes extension. When processing adjacent inline attribute blocks, the resolver walks through all siblings to find a target, resulting in O(N²) time complexity for N adjacent blocks. An attacker can trigger this worst-case behavior by submitting repeated attribute block patterns (e.g., {#a} repeated 8,000 times) without authentication or user interaction required. No configuration gating or allowlist validation prevents the quadratic walk. A fix is available in version 2.9.0 or later.

Affected products

League CommonMark 1.5.0 before 2.8.4

Timeline

2026-08-03: disclosed
2026-09-07: patched

References

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