What’s Vulnerable › Vulnerabilities

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

• Severity: low (CVSS 2.1 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-08 · updated 2026-10-25
• Weakness: CWE-434

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.

Affected products

• parse-community parse-server: from 9.0.0-alpha.1, < 9.9.1-alpha.11; before 8.6.81

References

• 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/pull/10505
• 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/9.9.1-alpha.11
• https://github.com/parse-community/parse-server/security/advisories/GHSA-v8x7-r927-cc93

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