CVE-2026-54889
Unsanitized URL schemes in MDEx Quill Delta output allow javascript: injection (XSS)
Description
Improper Neutralization of Input During Web Page Generation (XSS) vulnerability in leandrocp mdex allows cross-site scripting via unsanitized URL schemes in Quill Delta output. 'Elixir.MDEx':to_delta/2 converts Markdown into a Quill Delta. 'Elixir.MDEx.DeltaConverter':default_convert_node/3 in lib/mdex/delta_converter.ex copies the URL of a link, wikilink, or image node directly from the parsed Markdown into the Delta "link" or "image" attribute without applying a scheme allowlist or any normalization. An attacker who controls the Markdown text can supply a javascript: URL (for example [click](javascript:alert(document.cookie))) that survives verbatim into the Delta attribute. When the Delta is rendered to HTML by a downstream renderer (such as quill-delta-to-html or the Quill client), the attribute becomes an <a href> or <img src>, and the javascript: scheme executes in the browser of anyone who views the rendered content. The link and wikilink cases are the strongest vectors because javascript: in an href executes on click; the image case is lower impact because javascript: in <img src> generally does not execute in modern browsers. This issue affects mdex: from 0.8.3 before 0.13.2.
INFO
Published Date :
June 29, 2026, 8:17 p.m.
Last Modified :
June 30, 2026, 2:14 p.m.
Remotely Exploit :
Yes !
Source :
6b3ad84c-e1a6-4bf7-a703-f496b71e49db
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 4.0 | MEDIUM | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | ||||
| CVSS 4.0 | MEDIUM | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db |
Solution
- Update mdex to version 0.13.2 or later.
- Implement a URL scheme allowlist for all inputs.
- Sanitize all link and image URLs before rendering.
- Validate Markdown content for malicious scripts.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-54889.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-54889 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-54889
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-54889 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-54889 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 29, 2026
Action Type Old Value New Value Added Reference https://github.com/leandrocp/mdex/security/advisories/GHSA-4383-7xfp-gpph Added SSVC {'id': 'CVE-2026-54889', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-06-29T20:48:34.044130Z'} -
New CVE Received by 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
Jun. 29, 2026
Action Type Old Value New Value Added Affected [{'cpes': ['cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*'], 'repo': 'https://github.com/leandrocp/mdex', 'vendor': 'leandrocp', 'modules': ["'Elixir.MDEx'", "'Elixir.MDEx.DeltaConverter'"], 'product': 'mdex', 'versions': [{'status': 'affected', 'version': '0.8.3', 'lessThan': '0.13.2', 'versionType': 'semver'}], 'packageURL': 'pkg:hex/mdex', 'packageName': 'mdex', 'programFiles': ['lib/mdex.ex', 'lib/mdex/delta_converter.ex'], 'collectionURL': 'https://repo.hex.pm', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': "'Elixir.MDEx':to_delta/2"}, {'name': "'Elixir.MDEx.DeltaConverter':convert/2"}, {'name': "'Elixir.MDEx.DeltaConverter':default_convert_node/3"}]}, {'cpes': ['cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*'], 'repo': 'https://github.com/leandrocp/mdex', 'vendor': 'leandrocp', 'modules': ["'Elixir.MDEx'", "'Elixir.MDEx.DeltaConverter'"], 'product': 'mdex', 'versions': [{'status': 'affected', 'version': '9852db2456fdc9d856eb636603a7f608e22e3793', 'lessThan': '2817147f5b87ce7186aa604c9ee72499485b8f2f', 'versionType': 'git'}], 'packageURL': 'pkg:github/leandrocp/mdex', 'packageName': 'leandrocp/mdex', 'programFiles': ['lib/mdex.ex', 'lib/mdex/delta_converter.ex'], 'collectionURL': 'https://github.com', 'defaultStatus': 'unaffected', 'programRoutines': [{'name': "'Elixir.MDEx':to_delta/2"}, {'name': "'Elixir.MDEx.DeltaConverter':convert/2"}, {'name': "'Elixir.MDEx.DeltaConverter':default_convert_node/3"}]}] Added Description Improper Neutralization of Input During Web Page Generation (XSS) vulnerability in leandrocp mdex allows cross-site scripting via unsanitized URL schemes in Quill Delta output. 'Elixir.MDEx':to_delta/2 converts Markdown into a Quill Delta. 'Elixir.MDEx.DeltaConverter':default_convert_node/3 in lib/mdex/delta_converter.ex copies the URL of a link, wikilink, or image node directly from the parsed Markdown into the Delta "link" or "image" attribute without applying a scheme allowlist or any normalization. An attacker who controls the Markdown text can supply a javascript: URL (for example [click](javascript:alert(document.cookie))) that survives verbatim into the Delta attribute. When the Delta is rendered to HTML by a downstream renderer (such as quill-delta-to-html or the Quill client), the attribute becomes an <a href> or <img src>, and the javascript: scheme executes in the browser of anyone who views the rendered content. The link and wikilink cases are the strongest vectors because javascript: in an href executes on click; the image case is lower impact because javascript: in <img src> generally does not execute in modern browsers. This issue affects mdex: from 0.8.3 before 0.13.2. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-79 Added Reference https://cna.erlef.org/cves/CVE-2026-54889.html Added Reference https://github.com/leandrocp/mdex/commit/2817147f5b87ce7186aa604c9ee72499485b8f2f Added Reference https://github.com/leandrocp/mdex/security/advisories/GHSA-4383-7xfp-gpph Added Reference https://osv.dev/vulnerability/EEF-CVE-2026-54889