Postiz Has Unrestricted File Upload via MIME Type Spoofing that Leads to Stored XSS

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Summary

CVECVE-2026-40487
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-18 02:16:11 UTC
Updated2026-04-18 02:16:11 UTC
DescriptionPostiz is an AI social media scheduling tool. Prior to version 2.21.6, a file upload validation bypass allows any authenticated user to upload arbitrary HTML, SVG, or other executable file types to the server by spoofing the `Content-Type` header. The uploaded files are then served by nginx with a Content-Type derived from their original extension (`text/html`, `image/svg+xml`), enabling Stored Cross-Site Scripting (XSS) in the context of the application's origin. This can lead to session riding, account takeover, and full compromise of other users' accounts. Version 2.21.6 contains a fix.

Risk And Classification

Primary CVSS: v3.1 8.9 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:L

Problem Types: CWE-79 | CWE-345 | CWE-434 | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | CWE-345 CWE-345: Insufficient Verification of Data Authenticity | CWE-434 CWE-434: Unrestricted Upload of File with Dangerous Type

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8.9HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:L
3.1CNADECLARED8.9HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:L

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Gitroomhq Postiz-app affected < 2.21.6 Not specified

References

ReferenceSourceLinkTags
github.com/gitroomhq/postiz-app/security/advisories/GHSA-44wg-r34q-hvfx [email protected] github.com
github.com/gitroomhq/postiz-app/releases/tag/v2.21.6 [email protected] github.com
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