CVE-2026-126746: Composer/drupal/s3fs_cors vulnerability
The S3 File System CORS Upload module lets users upload files straight from the browser to Amazon S3 (or an S3-compatible service), using a file widget on entity forms.
The module doesn't sufficiently restrict the upload permission it gives the browser. A user who can upload through the widget can overwrite other files already stored in the bucket, including files they couldn't otherwise replace.
This vulnerability is mitigated by the fact that an attacker must have access to a form that uses the S3 File System CORS Upload widget.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/drupal/s3fs_corsto a version that resolves this vulnerability.Fixed in 1.4.0
Event History
Frequently Asked Questions
Who is exposed to this issue?
Users who can access an entity form containing the S3 File System CORS Upload widget may be able to exploit it. The issue is limited by the requirement that the attacker can upload through that widget.
What could an attacker do with the granted upload access?
They could overwrite files already stored in the configured Amazon S3 or S3-compatible bucket, including files they would not otherwise be allowed to replace.