# CVE-2026-54889: leandrocp mdex XSS in Quill Delta conversion

Source: https://junglewise.ai/threats/cve-2026-54889-leandrocp-mdex-xss-in-quill-delta-conversion  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-29. Updated: 2026-06-29  
License: CC BY 4.0 with a link back

CVE-2026-54889 · Severity: info · CVSS 5.1 · Published 2026-06-29

A vulnerability in the MDEx Markdown library for Elixir could allow attackers to execute malicious scripts in a user's browser. This occurs when the library processes Markdown containing specially crafted links and converts them into a format used by web editors. If an end-user clicks on one of these malicious links, it could lead to unauthorized actions or the theft of sensitive information like session cookies.

## Quick answers

**Is CVE-2026-54889 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-54889 being exploited in the wild.

**How severe is CVE-2026-54889?** Informational severity, with a CVSS score of 5.1, published 29 June 2026.

**Which products and versions are affected?** leandrocp mdex 0.8.3 to 0.13.1.

**Is there a fix for CVE-2026-54889?** A patch was published on 2026-06-29: Fixed in version 0.13.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-54889 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-54889?** 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

A Cross-Site Scripting (XSS) vulnerability exists in the 'Elixir.MDEx.DeltaConverter' module of the mdex library. The 'default_convert_node/3' function fails to sanitize or validate URL schemes when processing links, wikilinks, or images, allowing 'javascript:' URIs to be passed directly into the Quill Delta output. When this output is subsequently rendered into HTML by a downstream component (like a Quill client), the malicious URI is placed into 'href' or 'src' attributes. An attacker can exploit this by providing malicious Markdown that, when viewed and interacted with by a user, executes arbitrary JavaScript in the context of the user's session. The issue is fixed in version 0.13.2, which introduces default URL filtering.

## Affected products

- leandrocp mdex 0.8.3 to 0.13.1

## Timeline

- 2026-06-29: disclosed
- 2026-06-29: patched: Fixed in version 0.13.2
- 2026-06-29: advisory

## References

- [https://repo.hex.pm/](https://repo.hex.pm/)
- [https://github.com/](https://github.com/)
- [https://cna.erlef.org/cves/CVE-2026-54889.html](https://cna.erlef.org/cves/CVE-2026-54889.html)
- [https://github.com/leandrocp/mdex/commit/2817147f5b87ce7186aa604c9ee72499485b8f2f](https://github.com/leandrocp/mdex/commit/2817147f5b87ce7186aa604c9ee72499485b8f2f)
- [https://github.com/leandrocp/mdex/security/advisories/GHSA-4383-7xfp-gpph](https://github.com/leandrocp/mdex/security/advisories/GHSA-4383-7xfp-gpph)