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CVE-2026-55778

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

LOW
2.1
CVSS Score
Published: July 8, 2026 at 08:50 PM UTC
Updated: October 25, 2026 at 05:10 PM UTC
1 product affected across 1 vendorParse Server

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Severity
LOW2.1
Exploit prediction
EPSS 0.6%
SSVC
No known exploit

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Parse Server· Parse Communitynpm
90%
v < 8.6.81>= 9.0.0-alpha.1, < 9.9.1-alpha.11
Affected range stops below 8.6.81, so it looks safe — our inference, not a vendor statement
Affected range stops below 9.9.1-alpha.11, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet, and no fixed version or vendor advisory is recorded against it.

References (7)

x_refsource_CONFIRM
Source: cverecord
https://github.com/parse-community/parse-server/security/advisories/GHSA-v8x7-r927-cc93
x_refsource_MISC
Source: cverecord
https://github.com/parse-community/parse-server/pull/10505
x_refsource_MISC
Source: cverecord
https://github.com/parse-community/parse-server/pull/10506
x_refsource_MISC
Source: cverecord
https://github.com/parse-community/parse-server/commit/97c6a78d19f976ec756c1295f08a8fccab90799a
x_refsource_MISC
Source: cverecord
https://github.com/parse-community/parse-server/commit/be12a60d65b6e140481882037fb896b1f951df50
x_refsource_MISC
Source: cverecord
https://github.com/parse-community/parse-server/releases/tag/8.6.81
x_refsource_MISC
Source: cverecord
https://github.com/parse-community/parse-server/releases/tag/9.9.1-alpha.11

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

2.1LOWGitHub_M
Vector?

Quick Info

StatusDEFERRED
CWE
CWE-434

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