CVE-2026-55778
Parse Server: Stored XSS via non-standard file extension bypassing file upload extension blocklist
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
parse-servernpmDescription
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | parse-server | ≥ 9.0.0&&< 9.9.1-alpha.11 | 9.9.1-alpha.11 |
| 📦npm | parse-server | all versions | 8.6.81 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for parse-server. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update parse-server to 9.9.1-alpha.11 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55778 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-55778 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-55778. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-55778 in your dependencies?
O3 detects CVE-2026-55778 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.