fix: Stored XSS via non-standard file extension bypassing file upload extension blocklist (GHSA-v8x7-r927-cc93)

[mtrezza]

Issue

Stored XSS via non-standard file extension bypassing file upload extension blocklist (GHSA-v8x7-r927-cc93)

Tasks

• Add tests

[parse-github-assistant]

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[coderabbitai]

📝 Walkthrough

Walkthrough

FilesRouter.createHandler is refactored to separately derive the filename extension and the Content-Type header subtype, introducing a rejectExtension helper and using mime.getType to determine whether the filename extension is recognized. The blocklist is enforced on the filename extension unconditionally and on the content-type extension only as a fallback. Three new tests verify rejection of non-standard SVG/HTML filename variants and acceptance of a safe non-standard extension.

Changes

File Extension Blocklist Validation

Layer / File(s)	Summary
FilesRouter extension parsing and blocklist enforcement src/Routers/FilesRouter.js	Imports mime at the start of createHandler; adds a rejectExtension helper; separately parses extension from the filename and contentTypeExtension from the Content-Type subtype; applies the disabled-extension blocklist to extension first, then conditionally to contentTypeExtension only when mime does not recognize the filename extension.
Validation tests for non-standard filename extensions spec/ParseFile.spec.js	Adds three test cases: rejects multiple non-standard SVG filename variants (e.g., file.svg~, file.svg.tmp) with image/svg+xml content type; rejects non-standard HTML variants (e.g., file.html.old, file.html~) with text/html content type; accepts archive.bak with image/png content type.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• parse-community/parse-server#10383: Modifies FilesController.createFile MIME resolution and adds mismatch tests, directly overlapping with this PR's Content-Type vs. filename extension validation changes in the upload path.
• parse-community/parse-server#10191: Updates FilesRouter.createHandler extension derivation from the Content-Type header including MIME parameter/whitespace handling, which is the same code section refactored in this PR.
• parse-community/parse-server#10489: Adjusts filename extension/content-type derivation and blocklist enforcement in FilesRouter, with new tests for unusual extension variants — directly parallel to the changes in this PR.

🚥 Pre-merge checks | ✅ 6 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The pull request description is entirely missing. No content was provided addressing the required sections such as Issue, Approach, or Tasks outlined in the template.	Add a comprehensive pull request description following the template, including Issue (link to GHSA-v8x7-r927-cc93), Approach (explain the validation changes), and check completed Tasks.

✅ Passed checks (6 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Security Check	✅ Passed	The PR properly fixes XSS vulnerabilities (CVE-2026-30948, CVE-2026-31868) by validating both filename extensions and Content-Type headers. The fix prevents attackers from uploading dangerous files...
Engage In Review Feedback	✅ Passed	PR 10505 shows no review feedback comments or resolved discussions in git history. Without feedback to engage with, the requirement to "engage in review feedback" is not applicable.
Title check	✅ Passed	The pull request title begins with the required 'fix:' prefix and clearly describes the main security fix addressing a stored XSS vulnerability via non-standard file extensions.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.62%. Comparing base (30f1612) to head (7885d88).

Additional details and impacted files

@@            Coverage Diff             @@
##            alpha   #10505      +/-   ##
==========================================
- Coverage   92.62%   92.62%   -0.01%     
==========================================
  Files         193      193              
  Lines       16947    16954       +7     
  Branches      240      240              
==========================================
+ Hits        15698    15703       +5     
- Misses       1226     1228       +2     
  Partials       23       23              

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[parseplatformorg]

🎉 This change has been released in version 9.9.1-alpha.11