Stored XSS via MIME-spoofed file uploads
Published Apr 18, 2026 · Updated Apr 18, 2026
Stored XSS in Postiz before 2.21.6 allows remote authenticated users to compromise other accounts through uploaded executable files. The upload pipeline trusted the multipart Content-Type and original filename instead of inspecting file bytes, while nginx derived a browser-executable type from the stored extension. A victim must follow the attacker's upload link; the persistent public file can act with the victim's session to gain team-admin access, delete posts and integrations, or impersonate the victim through the API.
Summary
What happened
Stored XSS in Postiz before 2.21.6 allows remote authenticated users to compromise other accounts through uploaded executable files. The upload pipeline trusted the multipart Content-Type and original filename instead of inspecting file bytes, while nginx derived a browser-executable type from the stored extension. A victim must follow the attacker's upload link; the persistent public file can act with the victim's session to gain team-admin access, delete posts and integrations, or impersonate the victim through the API.
The record
- CVE
- CVE-2026-40487
- Published
- Apr 18, 2026
- Updated
- Apr 18, 2026
- Vendor
- GitroomHQ
- Product
- Postiz
- Classifications
- CWE-79, CWE-434, CWE-345, T1189
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 18, 2026CVE publishedPublication date reported by the CVE source.
- Apr 18, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 2.21.6
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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