DRUPAL-CONTRIB-2026-279: Composer/drupal/s3fs vulnerability
S3 File System (s3fs) provides an additional file system to your Drupal site that stores files in Amazon's Simple Storage Service (S3) storage.
The module doesn't sufficiently isolate upload context between separate object(file) operations in the same request resulting in the potential for objects to be uploaded with incorrect access control list (ACL) entries or corruption through incorrect operation metadata.
This vulnerability is mitigated by the fact that an attacker must be able to trigger multiple file operations on S3FS.
Some vectors are mitigated by:
Not enabling private:// takeover ($settings['s3fs.uses3forprivate'] = FALSE;) or only enabled with $settings['s3fs.uploadasprivate'] = TRUE; The deployment does not utilize hooks3fsstreamopenparamsalter(), hooks3fsuploadparamsalter(), hooks3fscopyparamsalter(), or hooks3fscommandparamsalter()
If both points above have always been true, all currently known vectors are mitigated.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/drupal/s3fsto a version that resolves this vulnerability.Fixed in 3.12.0 - Configuration
Do not enable private:// takeover; set $settings['s3fs.use_s3_for_private'] = FALSE.
Drupal S3 File System (s3fs) $settings['s3fs.use_s3_for_private'] = FALSE - Configuration
If private:// takeover is enabled, set $settings['s3fs.upload_as_private'] = TRUE.
Drupal S3 File System (s3fs) $settings['s3fs.upload_as_private'] = TRUE