Stored XSS via extension-only image validation
Published Jul 10, 2026 · Updated Jul 10, 2026
Stored XSS in affected Drupal core releases allows remote authenticated users to upload active content through JSON:API or REST image fields. Image validation accepts an allowed image extension without verifying that the uploaded bytes have an image MIME type. Exploitation requires upload permission, a web-server configuration that serves the file by its actual type, and a user who opens it, enabling script execution in that user’s browser.
Summary
What happened
Stored XSS in affected Drupal core releases allows remote authenticated users to upload active content through JSON:API or REST image fields. Image validation accepts an allowed image extension without verifying that the uploaded bytes have an image MIME type. Exploitation requires upload permission, a web-server configuration that serves the file by its actual type, and a user who opens it, enabling script execution in that user’s browser.
The record
- CVE
- CVE-2026-55808
- Published
- Jul 10, 2026
- Updated
- Jul 10, 2026
- Vendor
- Avatar Uploader Project
- Product
- Drupal core
- Classifications
- CWE-79, CAPEC-63, T1059.007
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Jul 10, 2026CVE publishedPublication date reported by the CVE source.
- Jul 10, 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=0.0.0 <10.5.12
- Affected versionversion=0.0.0 <11.0.*
- Affected versionversion=0.0.0 <11.1.*
- Affected versionversion=10.6.0 <10.6.11
- Affected versionversion=11.2.0 <11.2.14
- Affected versionversion=11.3.0 <11.3.12
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.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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