CVE-2025-46734
league/commonmark contains a XSS vulnerability in Attributes extension
Impact
### 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 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: ```md ![](){onerror=alert(1)} ``` Which results in the following HTML: ```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](https://commonmark.thephpleague.com/2.7/extensions/attributes/#configuration) - 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](https://commonmark.thephpleague.com/security/#additional-filtering)
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| composer | league/commonmark | >= 1.5.0, < 2.7.0 | 2.7.0 |
Affected products
| Product | Affected versions |
|---|---|
| League/Commonmark Library (Versions 1.5.0 | through 2.6.x |
Versions were read from the advisory text. No structured product data has been published for this record yet.
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/thephpleague/commonmark/commit/f0d626cf05ad3e99e6db26ebcb9091b6cd1cd89b
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-3527-qv2q-pfvx
- https://github.com/advisories/GHSA-3527-qv2q-pfvx
- https://nvd.nist.gov/vuln/detail/CVE-2025-46734