# CVE-2026-35200: Parse Server stored XSS via Content-Type mismatch in file uploads

Source: https://junglewise.ai/threats/cve-2026-35200-parse-server-stored-xss-via-content-type-mismatch-in-file-uploads  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-06. Updated: 2026-07-24  
License: CC BY 4.0 with a link back

CVE-2026-35200 · Severity: medium · CVSS 5.4 · Published 2026-04-06

Parse Server, an open-source backend for Node.js applications, contains a vulnerability in how it handles file uploads. An attacker can upload a file that appears harmless (like a text file) but is actually treated as a malicious web page (HTML) by the storage system. This could allow an attacker to perform cross-site scripting (XSS) attacks, potentially leading to the theft of user session data or unauthorized actions on the platform.

Technologies: [parse-server (npm)](https://junglewise.ai/threats/technologies/parse-server). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-35200 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-35200 being exploited in the wild.

**How severe is CVE-2026-35200?** Medium severity, with a CVSS score of 5.4, published 6 April 2026.

**Which products and versions are affected?** parse-server (npm) SEMVER:introduced=9.0.0,fixed=9.7.1-alpha.4.

**Is there a fix for CVE-2026-35200?** Yes. parse-server (npm): upgrade to 9.7.1-alpha.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-35200 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-35200?** Check whether you run parse-server (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- parse-server (npm): upgrade to 9.7.1-alpha.4 or later

  ```sh
  npm install parse-server@9.7.1-alpha.4
  ```


## Technical details

A vulnerability exists in Parse Server's FilesController where the 'Content-Type' header provided during a file upload is not validated against the file's extension. An attacker with upload privileges can bypass extension allowlists by providing a permitted extension (e.g., .txt) while specifying a different MIME type (e.g., text/html) in the header. When using storage adapters that rely on the stored metadata to serve files (such as Amazon S3 or Google Cloud Storage), the file is served with the attacker-controlled MIME type, enabling stored XSS. The default GridFS adapter is unaffected as it derives MIME types from filenames at request time. The fix ensures the Content-Type is derived from the file extension, overriding user-provided headers.

## Affected products

- Parse Platform Parse Server < 8.6.73, >= 9.0.0 < 9.7.1-alpha.4

## Identifiers

- CVE-2026-35200
- GHSA-vr5f-2r24-w5hc

## Timeline

- 2026-04-02: patched: Fixes merged in PR #10383 and #10384
- 2026-04-06: disclosed: Initial advisory published
- 2026-04-06: advisory: NVD published CVE-2026-35200

## References

- [https://github.com/parse-community/parse-server/pull/10383](https://github.com/parse-community/parse-server/pull/10383)
- [https://github.com/parse-community/parse-server/pull/10384](https://github.com/parse-community/parse-server/pull/10384)
- [https://github.com/parse-community/parse-server/security/advisories/GHSA-vr5f-2r24-w5hc](https://github.com/parse-community/parse-server/security/advisories/GHSA-vr5f-2r24-w5hc)

## Related threats

- [Duplicate Advisory: Parse Server vulnerable to stored XSS via malformed Content-Type bypassing file upload extension blocklist](https://junglewise.ai/threats/duplicate-advisory-parse-server-vulnerable-to-stored-xss-via-malformed-00d8867c)
- [Parse Server stored XSS via malformed Content-Type bypass](https://junglewise.ai/threats/cve-2026-61448-parse-server-stored-xss-via-malformed-content-type-bypass)
- [Parse Server information disclosure in LiveQuery ACL transitions](https://junglewise.ai/threats/cve-2026-57481-parse-server-information-disclosure-in-livequery-acl-transitions)
- [Parse Community Parse Server denial of service via nested query operators](https://junglewise.ai/threats/cve-2026-57480-parse-community-parse-server-denial-of-service-via-nested-query)
- [Parse Server stored XSS via file upload extension bypass](https://junglewise.ai/threats/cve-2026-55778-parse-server-stored-xss-via-file-upload-extension-bypass)