md-editor-v3: XSS via fenced-code language rendering bypass
Published Sep 18, 2026 · Updated Nov 3, 2026
Original summary
Normalized public record · Updated Nov 3, 2026
md-editor-v3: XSS via fenced-code language rendering bypass
Publisher and source text is retained separately from QFinch interpretation.
QFinch assessment
MdPreview interpolates a fenced-code language into HTML attributes without escaping it. A crafted info string therefore executes JavaScript even when the shipped XSSPlugin is enabled.
Potential impact
An attacker who can supply Markdown can execute JavaScript in the application origin when a victim renders it. If the host stores that Markdown, this becomes stored XSS.
Technical context
useMarkdownIt() (packages/MdEditor/layouts/Content/composition/useMarkdownIt.ts:206) registers a highlight callback whose final return inserts language into both class="language-${language}" and an unquoted language=${language} attribute without escaping. Both highlighting paths reach this return. XSSPlugin() filters only existing htmlblock and htmlinline tokens before rendering, so it cannot inspect this renderer-generated HTML.
Evidence: public source recordsAffected products
| Affected package, product or range | Fix status |
|---|---|
| Consult the referenced vendor advisory for affected versions. | Consult source advisory |
Matching a version is only one part of assessing exposure. QFinch has not assessed your environment on this public page.
Remediation
Apply the vendor-supported fixed release or mitigation, then verify the affected component is no longer reachable.
- Confirm the affected product and reachable code path exist in your environment.
- Apply the vendor-supported patch or mitigation from the primary advisory.
- Rescan the exact deployed revision and retain verification evidence.
Evidence coverage
- SSVC priority
- LOW
- Confidence
- Not available
- Aliases
- None reported
Scores appear only when corresponding evidence exists. Missing data is never interpreted as zero risk.
Sources and record history
Record history
Published Sep 18, 2026 · Last refreshed Nov 3, 2026