# CVE-2026-77611: SeaweedFS S3 object-scope bypass in PutObjectAcl

Source: https://junglewise.ai/threats/cve-2026-77611-seaweedfs-s3-object-scope-bypass-in-putobjectacl  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-26. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-77611 · Severity: high · CVSS 7.1 · Published 2026-08-26

SeaweedFS is a distributed storage system that provides S3-compatible object storage. An authenticated user with limited permissions to access files in a specific folder can bypass those restrictions and overwrite different files at higher levels of the storage hierarchy, potentially corrupting or replacing critical data that should be protected from that user.

Technologies: [SeaweedFS](https://junglewise.ai/threats/technologies/seaweedfs). Vendors: [SeaweedFS](https://junglewise.ai/threats/vendors/seaweedfs).

## Quick answers

**Is CVE-2026-77611 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-77611 being exploited in the wild.

**How severe is CVE-2026-77611?** High severity, with a CVSS score of 7.1, published 26 August 2026.

**Which products and versions are affected?** SeaweedFS < 4.40.

**Is there a fix for CVE-2026-77611?** A patch was published on 2026-07-14: Fix committed to repository; version 4.40 includes the patch Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-77611 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-77611?** Check whether you run SeaweedFS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

This is an authorization bypass vulnerability in the S3 PutObjectAcl handler. The vulnerability occurs because the handler authorizes ACL modification requests against the correctly scoped object key (e.g., allowed/protected.txt) but then writes the updated entry back to the bucket root directory instead of the object's actual parent directory. When an authenticated principal with scoped write permissions calls PutObjectAcl on a nested key, the full object entry (including content, metadata, owner, and ACL) is written to an object with the same basename at the bucket root, overwriting any existing object there. This requires authentication and S3 credentials configured with specific scope permissions, but allows a scoped user to overwrite objects they should not have access to. The vulnerability is fixed in version 4.40 and later.

## Affected products

- SeaweedFS SeaweedFS < 4.40

## Timeline

- 2026-08-26: disclosed
- 2026-07-14: patched: Fix committed to repository; version 4.40 includes the patch

## References

- [https://github.com/seaweedfs/seaweedfs/commit/311bc3a6dfbd042751692bc3de8accc516fcf8c1](https://github.com/seaweedfs/seaweedfs/commit/311bc3a6dfbd042751692bc3de8accc516fcf8c1)
- [https://github.com/seaweedfs/seaweedfs/security/advisories/GHSA-9x53-cjpr-m682](https://github.com/seaweedfs/seaweedfs/security/advisories/GHSA-9x53-cjpr-m682)

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