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TI-2026-39662 Aliases CVE-2026-54889

Unsanitized URL schemes in MDEx Quill Delta output allow javascript: injection (XSS)

Priority MEDIUM 56CWE-79Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Active
Attack complexity
Low
Attack requirements
None
Impact type
Cross-site scripting
Confidentiality · integrity · availability
Low · Low · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-79.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00393 33rd percentileScored 2026-11-07
Fix Fixed mdex (leandrocp): 0.13.2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
leandrocpmdex0.8.3 to before 0.13.20.13.2Patch availableCNA
  • mdex Vendorleandrocp Affected 0.8.3 to before 0.13.2 Fixed in 0.13.2 Patch available CNA

CPE names CNA · 1

CPEVersionsRoleVendor
cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:*——leandrocp
  • cpe:2.3:a:leandrocp:mdex:*:*:*:*:*:*:*:* Versions — — ·leandrocp

Remediation

  • Fix · CNA mdex (leandrocp) Fixed in 0.13.2

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    leandrocp mdex 0.13.2

    2 records Highest priority Priority MEDIUM 1 MEDIUM, 1 LOW

    Other records, highest priority first

    • TI-2026-38508 Atom-table exhaustion denial-of-service via JSON parse_document in MDExPriority LOW 35
    Show all 2 records →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-54889

References

Patch 1

Advisory 1

Other 2

  • TI-2026-39661 Uncontrolled recursion over deeply nested Markdown crashes the BEAM in mdex CVSS 4.0MEDIUM 6.9
  • TI-2026-38511 Unbounded native memory leak in mdex escaped-tag rendering enables unauthenticated denial of service CVSS 4.0MEDIUM 6.9
  • TI-2026-38508 Atom-table exhaustion denial-of-service via JSON parse_document in MDEx CVSS 4.0HIGH 8.2
  • TI-2026-38510 Unbounded memory allocation in highlight_lines range expansion in mdex CVSS 4.0MEDIUM 6.9
  • TI-2026-38509 Cross-site scripting in MDEx via unescaped highlight_lines_class code-fence attribute CVSS 4.0LOW 2.3

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences