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CVE-2025-46734

league/commonmark Cross-site Scripting vulnerability in Attributes extension

MEDIUM
6.4
CVSS Score
Published: May 5, 2025 at 07:52 PM UTC
Updated: June 17, 2026 at 09:26 AM UTC
1 product affected across 1 vendorCommonmark

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Severity
MEDIUM6.4
Exploit prediction
EPSS 0.4%
SSVC
No known exploit

Description

league/commonmark is a PHP Markdown parser. A 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. 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. 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; and manually-added `href` and `src` attributes now respect the existing `allow_unsafe_links` configuration option. If upgrading is not feasible, please consider disabling the `AttributesExtension` for untrusted users and/or filtering the rendered HTML through a library like HTMLPurifier.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Commonmark· Thephpleague
60%
v < 2.7.0
Affected range stops below 2.7.0, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet, and no fixed version or vendor advisory is recorded against it.

References (2)

x_refsource_MISC
Source: [email protected]
https://github.com/thephpleague/commonmark/commit/f0d626cf05ad3e99e6db26ebcb9091b6cd1cd89b
x_refsource_CONFIRM
Source: [email protected]
https://github.com/thephpleague/commonmark/security/advisories/GHSA-3527-qv2q-pfvx

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.4MEDIUMGitHub_M
Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
NONE
Scope
CHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusDEFERRED
CWE
CWE-79

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