How severe is GHSA-3527-qv2q-pfvx?

GHSA-3527-qv2q-pfvx has a CVSS score of 6.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by GHSA-3527-qv2q-pfvx?

GHSA-3527-qv2q-pfvx affects the following packages: league/commonmark (Packagist). Ecosystems affected: Packagist.

How do I fix GHSA-3527-qv2q-pfvx?

Update league/commonmark to 2.7.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3527-qv2q-pfvx is resolved across your whole dependency graph.

How do I detect GHSA-3527-qv2q-pfvx in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for league/commonmark, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-3527-qv2q-pfvx if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is GHSA-3527-qv2q-pfvx actively exploited in the wild?

No public exploit code has been indexed for GHSA-3527-qv2q-pfvx yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-3527-qv2q-pfvx?

GHSA-3527-qv2q-pfvx has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 33th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-3527-qv2q-pfvx?

GHSA-3527-qv2q-pfvx is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was GHSA-3527-qv2q-pfvx published, and has it been updated?

GHSA-3527-qv2q-pfvx was published on May 5, 2025 and was last updated on March 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘

🐘 Packagist

Not in CISA KEV

MEDIUM severity

league/commonmark contains a XSS vulnerability in Attributes extensionGHSA-3527-qv2q-pfvx

MEDIUMFix: thephpleague/commonmark@f0d626c

GHSA-3527-qv2q-pfvx is a medium-severity (CVSS 6.4) Cross-site Scripting (XSS) vulnerability in league/commonmark. A fix is available for league/commonmark — see the affected versions and patch details below.

Also known asCVE-2025-46734

Published

May 5, 2025

Updated

Mar 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-3527-qv2q-pfvx.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk+0.01%

Lower risk than most CVEs33th percentile — riskier than 33% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐘league/commonmark

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

Summary

Cross-site scripting (XSS) vulnerability in the Attributes extension of the league/commonmark library (versions 1.5.0 through 2.6.x) allows remote attackers to insert malicious JavaScript calls into HTML.

Details

The league/commonmark library provides configuration options such as html_input: 'strip' and allow_unsafe_links: false to mitigate cross-site scripting (XSS) attacks by stripping raw HTML and disallowing unsafe links. However, when the Attributes Extension is enabled, it introduces a way for users to inject arbitrary HTML attributes into elements via Markdown syntax using curly braces.

As a result, even with the secure configuration shown above, an attacker can inject dangerous attributes into applications using this extension via a payload such as:

![](){onerror=alert(1)}

Which results in the following HTML:

<p><img onerror="alert(1)" src="" alt="" /></p>

Which causes the JS to execute immediately on page load.

Patches

Version 2.7.0 contains three changes to prevent this XSS attack vector:

All attributes starting with on are considered unsafe and blocked by default
Support for an explicit allowlist of allowed HTML attributes
Manually-added href and src attributes now respect the existing allow_unsafe_links configuration option

Workarounds

If upgrading is not feasible, please consider:

Disabling the AttributesExtension for untrusted users
Filtering the rendered HTML through a library like HTMLPurifier

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`league/commonmark`	≥ 1.5.0&&< 2.7.0	2.7.0`composer require league/commonmark:^2.7.0`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for league/commonmark, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update league/commonmark to 2.7.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3527-qv2q-pfvx is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

### Summary Cross-site scripting (XSS) vulnerability in the [Attributes extension](https://commonmark.thephpleague.com/extensions/attributes/) of the league/commonmark library (versions 1.5.0 through 2.6.x) allows remote attackers to insert malicious JavaScript calls into HTML. ### Details The league/commonmark library provides configuration options such as `html_input: 'strip'` and `allow_unsafe_links: false` to mitigate cross-site scripting (XSS) attacks by stripping raw HTML and disallowing unsafe links. However, when the Attributes Extension is enabled, it introduces a way for users to i