# CVE-2026-55778: Parse Server stored XSS via file upload extension bypass

Source: https://junglewise.ai/threats/cve-2026-55778-parse-server-stored-xss-via-file-upload-extension-bypass  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-08. Updated: 2026-07-08  
License: CC BY 4.0 with a link back

CVE-2026-55778 · Severity: medium · CVSS 4 · Published 2026-07-08

Parse Server, a popular open-source backend for Node.js applications, contains a security flaw in how it handles file uploads. An attacker can bypass security filters by using unusual file extensions to upload malicious files, such as scripts disguised as images. If these files are then accessed by other users, it could lead to unauthorized actions or data theft within the context of the application.

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

## Quick answers

**Is CVE-2026-55778 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-55778 being exploited in the wild.

**How severe is CVE-2026-55778?** Medium severity, with a CVSS score of 4, published 8 July 2026.

**Which products and versions are affected?** parse-server (npm) SEMVER:introduced=9.0.0,fixed=9.9.1-alpha.11.

**Is there a fix for CVE-2026-55778?** Yes. parse-server (npm): upgrade to 9.9.1-alpha.11 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-55778 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-55778?** 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 9.9.1-alpha.11 or later

  ```sh
  npm install parse-server@9.9.1-alpha.11
  ```


## Technical details

A vulnerability in Parse Server's 'fileUpload.fileExtensions' blocklist allows attackers to bypass extension restrictions. By uploading files with non-standard or compound extensions (e.g., double extensions) and a dangerous MIME type, attackers can trick storage adapters like Amazon S3 or Google Cloud Storage into serving active content. This results in stored cross-site scripting (XSS) when the file is rendered in a victim's browser. The issue is rooted in insufficient validation of file extensions against the default blocklist. Patches are available in versions 9.9.1-alpha.11 and 8.6.81.

## Affected products

- parse-community parse-server >= 9.0.0-alpha.1, < 9.9.1-alpha.11; < 8.6.81

## Identifiers

- CVE-2026-55778
- GHSA-v8x7-r927-cc93

## Timeline

- 2026-06-16: patched: Fixes committed to repository
- 2026-07-08: disclosed: CVE published

## References

- [https://github.com/parse-community/parse-server/commit/97c6a78d19f976ec756c1295f08a8fccab90799a](https://github.com/parse-community/parse-server/commit/97c6a78d19f976ec756c1295f08a8fccab90799a)
- [https://github.com/parse-community/parse-server/commit/be12a60d65b6e140481882037fb896b1f951df50](https://github.com/parse-community/parse-server/commit/be12a60d65b6e140481882037fb896b1f951df50)
- [https://github.com/parse-community/parse-server/pull/10505](https://github.com/parse-community/parse-server/pull/10505)
- [https://github.com/parse-community/parse-server/pull/10506](https://github.com/parse-community/parse-server/pull/10506)
- [https://github.com/parse-community/parse-server/releases/tag/8.6.81](https://github.com/parse-community/parse-server/releases/tag/8.6.81)
- [https://github.com/parse-community/parse-server/releases/tag/9.9.1-alpha.11](https://github.com/parse-community/parse-server/releases/tag/9.9.1-alpha.11)
- [https://github.com/parse-community/parse-server/security/advisories/GHSA-v8x7-r927-cc93](https://github.com/parse-community/parse-server/security/advisories/GHSA-v8x7-r927-cc93)

## 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 supply chain compromise via unreviewed version tags](https://junglewise.ai/threats/cve-2021-47986-parse-server-supply-chain-compromise-via-unreviewed-version-tags)