GHSA-g2gp-3wwq-f4ph: league/commonmark Denial of Service Vulnerability

HIGH
Share
CVSS 7.5
CWE-407
Published
Advisory Summary

GHSA-g2gp-3wwq-f4ph is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-407: Inefficient Algorithmic Complexity) affecting league/commonmark libraries in the Packagist ecosystem. The issue involves denial of service via adjacent inline attribute blocks. Remediation is available by upgrading affected packages to version 2.9.0.

GHSA-g2gp-3wwq-f4ph at a Glance

CVE Identifier N/A
GHSA Identifier GHSA-g2gp-3wwq-f4ph
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-407: Inefficient Algorithmic Complexity
Affected Product league/commonmark
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix GHSA-g2gp-3wwq-f4ph

To remediate this vulnerability, upgrade all affected league/commonmark dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

league/commonmark fixed: 2.9.0 
Upgrade league/commonmark to 2.9.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for league/commonmark

How to Check if You Are Affected

To determine whether your application is affected by GHSA-g2gp-3wwq-f4ph, inspect your project dependencies for league/commonmark:

inspect dependencies for league/commonmark

Analyze the terminal output to locate any version of league/commonmark in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.9.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-407: Inefficient Algorithmic Complexity, where an algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached. In league/commonmark, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact With the Attributes extension enabled, `AttributesListener::findTargetAndDirection()` resolves each attribute node's target by walking outward through its siblings. For a run of N adjacent inline attribute blocks placed at the start of a block (with nothing to their left), each node scans the **entire** sibling list to the far-right end before giving up and falling back to the parent. Each resolution is therefore Θ(N) and the whole run is **Θ(N²)**. Reaching the path requires `AttributesExtension` (opt-in, but first-party: `League\CommonMark\Extension\Attributes\AttributesExtension`). No other configuration matters — the quadratic walk runs unconditionally during parsing and is **not** gated by the `attributes/allow` allow-list, the `on*` hardening added in 2.7.0, or `allow_unsafe_links`. An unauthenticated attacker can submit a **~32 KB** input (`{#a}` repeated 8,000 times) that takes **over 5 seconds** to convert, with time growing quadratically in input length — a cheap denial of service. Availability impact only. **The Attributes extension was introduced in 1.5.0 (May 2020) with this outward-walk resolver present from the first commit, so all releases from 1.5.0 onward (including every 2.x) are affected.** ### Workarounds There is no library-level configuration that gates the quadratic walk. Integrators who cannot upgrade can only reduce exposure indirectly: - **Disable the Attributes extension** for untrusted input, or - **Impose a strict maximum input length before conversion** — noting that because the cost is quadratic, even a modest cap must be small to meaningfully bound worst-case CPU. Upgrading to a release containing the fix is recommended.

GHSA-g2gp-3wwq-f4ph Affected league/commonmark Versions

1 component(s)
Fixed Versions:
2.9.0
Product / Package Ecosystem Affected Versions Fixed Version
league/commonmark
 Packagist
≥ 1.5.0
< 2.9.0
2.9.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/thephpleague/commonmark/security/advisories/GHSA-g2gp-3wwq-f4ph
Security Fix Commit FIX COMMIT
https://github.com/thephpleague/commonmark/commit/2d4c0fafa62501be919262064cffa6d71687430b
league/commonmark Source Repository REPOSITORY
https://github.com/thephpleague/commonmark
league/commonmark Release RELEASE
https://github.com/thephpleague/commonmark/releases/tag/2.9.0

Frequently Asked Questions

What is GHSA-g2gp-3wwq-f4ph?
GHSA-g2gp-3wwq-f4ph is a security vulnerability in league/commonmark involving Denial of service via adjacent inline attribute blocks under CWE-407: Inefficient Algorithmic Complexity.
Which league/commonmark versions are affected?
Affected versions include releases prior to 2.9.0 across affected packages: league/commonmark.
What version fixes GHSA-g2gp-3wwq-f4ph?
Upgrading to 2.9.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is league/commonmark affected?
Yes, league/commonmark is affected in releases prior to 2.9.0. Upgrade your dependency to 2.9.0 or later.
What is the CVSS score of GHSA-g2gp-3wwq-f4ph?
GHSA-g2gp-3wwq-f4ph has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with GHSA-g2gp-3wwq-f4ph?
GHSA-g2gp-3wwq-f4ph is classified under CWE-407: Inefficient Algorithmic Complexity (An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.).
How can I check Packagist dependencies for GHSA-g2gp-3wwq-f4ph?
Run the dependency tree command: 'inspect dependencies for league/commonmark'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g2gp-3wwq-f4ph",
  "modified" : "2026-08-06T20:39:52Z",
  "published" : "2026-08-06T20:39:52Z",
  "aliases" : [ ],
  "summary" : "league/commonmark: Denial of service via adjacent inline attribute blocks",
  "details" : "### Impact\n\nWith the Attributes extension enabled, `AttributesListener::findTargetAndDirection()` resolves each attribute node's target by walking outward through its siblings. For a run of N adjacent inline attribute blocks placed at the start of a block (with nothing to their left), each node scans the **entire** sibling list to the far-right end before giving up and falling back to the parent. Each resolution is therefore Θ(N) and the whole run is **Θ(N²)**.\n\nReaching the path requires `AttributesExtension` (opt-in, but first-party: `League\\CommonMark\\Extension\\Attributes\\AttributesExtension`). No other configuration matters — the quadratic walk runs unconditionally during parsing and is **not** gated by the `attributes/allow` allow-list, the `on*` hardening added in 2.7.0, or `allow_unsafe_links`. An unauthenticated attacker can submit a **~32 KB** input (`{#a}` repeated 8,000 times) that takes **over 5 seconds** to convert, with time growing quadratically in input length — a cheap denial of service. Availability impact only. **The Attributes extension was introduced in 1.5.0 (May 2020) with this outward-walk resolver present from the first commit, so all releases from 1.5.0 onward (including every 2.x) are affected.**\n\n### Workarounds\n\nThere is no library-level configuration that gates the quadratic walk. Integrators who cannot upgrade can only reduce exposure indirectly:\n\n- **Disable the Attributes extension** for untrusted input, or\n- **Impose a strict maximum input length before conversion** — noting that because the cost is quadratic, even a modest cap must be small to meaningfully bound worst-case CPU.\n\nUpgrading to a release containing the fix is recommended.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "league/commonmark"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.5.0"
      }, {
        "fixed" : "2.9.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/thephpleague/commonmark/security/advisories/GHSA-g2gp-3wwq-f4ph"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/thephpleague/commonmark/commit/2d4c0fafa62501be919262064cffa6d71687430b"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/thephpleague/commonmark"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/thephpleague/commonmark/releases/tag/2.9.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-407" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-06T20:39:52Z",
    "nvd_published_at" : null
  }
}