Parse Server vulnerable to stored XSS via malformed Content-Type bypassing file upload extension blocklist

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

2.1 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N · score source

EPSS

• CVE-2026-61448: 0.41% estimated exploitation activity in the next 30 days; percentile 35.81 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Parse Server's file upload validation uses the `fileUpload.fileExtensions` option (enabled by default with a blocklist) to reject files that browsers may render as active content, mitigating stored cross-site scripting (XSS). When an uploaded file's extension is not recognized by the `mime` package, Parse Server preserves the client-supplied `Content-Type` and passes it to the storage adapter. A malformed `Content-Type` that is not a valid `type/subtype` media type — for example `image` (no subtype), `image/` (empty subtype), or `image//svg+xml` (invalid token) — bypassed the blocklist and was stored unchanged. On storage adapters that persist and serve the uploaded `Content-Type` (such as Amazon S3, Google Cloud Storage, or Azure Blob Storage), a browser cannot parse the malformed `Content-Type` and falls back to MIME-sniffing the file content; a file whose body begins with HTML markup is then rendered as HTML, executing any embedded script in the application's origin.…

Published by the source

29 Oct 2026, 16:33 UTC

Last modified by the source

29 Oct 2026, 16:45 UTC

Source last checked

30 Oct 2026, 06:00 UTC

1. Revision 2 · amended · 30 Oct 2026

   Amended from osv record GHSA-r899-h629-j84r

2. Revision 1 · created · 29 Oct 2026

   Published from ghsa record GHSA-r899-h629-j84r

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# Patch Next advisory brief: CVE-2026-61448

Advisory: Parse Server vulnerable to stored XSS via malformed Content-Type bypassing file upload extension blocklist
IDs: CVE-2026-61448, GHSA-r899-h629-j84r
Record: https://patchnext.com/advisories/cve-2026-61448 (revision 2, source checked 30 Oct 2026, 06:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: parse-server 9.10.0-alpha.2, 8.6.84. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm parse-server: affected >= 9.0.0, < 9.10.0-alpha.2; < 8.6.84; fixed in 9.10.0-alpha.2, 8.6.84

## Suggested inspection (read-only)
- `npm ls parse-server --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on parse-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-r899-h629-j84r (GitHub-reviewed advisory GHSA-r899-h629-j84r lists affected ranges: npm parse-server >=9.0.0 =0 <=8.6.83)
- Verified: https://osv.dev/vulnerability/GHSA-r899-h629-j84r (OSV record GHSA-r899-h629-j84r lists affected ranges: npm parse-server >=9.0.0 =0 <8.6.84 (fixed))

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