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CVE-2026-55874: CVE-2026-55874: Cross-Bucket Path Traversal in SeaweedFS S3 API Gateway

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CVE-2026-55874: Cross-Bucket Path Traversal in SeaweedFS S3 API Gateway

Vulnerability ID: CVE-2026-55874
CVSS Score: 7.7
Published: 2026-08-28

A critical path traversal vulnerability (CVE-2026-55874) in the SeaweedFS S3 API Gateway prior to version 4.34 allows authenticated remote attackers with write access to at least one bucket to bypass isolation. By supplying crafted directory traversal sequences in the X-Amz-Copy-Source header, an attacker can read objects from arbitrary buckets on the same deployment.

TL;DR

SeaweedFS S3 API Gateway allows cross-bucket reads via path traversal in the X-Amz-Copy-Source header prior to version 4.34.

⚠️ Exploit Status: POC

Technical Details

  • CWE ID: CWE-22
  • Attack Vector: Network
  • CVSS Score: 7.7
  • EPSS Score: 0.00606
  • Exploit Status: poc
  • CISA KEV Status: Not Listed

Affected Systems

  • SeaweedFS
  • SeaweedFS: < 4.34 (Fixed in: 4.34)

Code Analysis

Commit: b44cf51

S3 API: reject path traversal in X-Amz-Copy-Source header

Exploit Details

  • Official Test Suite: Regression test cases validating the behavior of the S3 copy source path traversal payloads.

Mitigation Strategies

  • Upgrade SeaweedFS to version 4.34 or later to address the vulnerability in the codebase.
  • Deploy Web Application Firewall (WAF) rules targeting the X-Amz-Copy-Source header to filter and block path traversal sequences.
  • Audit historic S3 access logs and reverse proxy logs for requests involving parent directory segments in copy handlers.

Remediation Steps:

  1. Identify all deployed SeaweedFS S3 API Gateway instances.
  2. Schedule maintenance windows to deploy SeaweedFS version 4.34 or higher.
  3. If immediate upgrade is impossible, write a custom WAF signature or Nginx rule to check the X-Amz-Copy-Source header for path-traversal strings.
  4. Verify blocking efficacy with standard S3 testing utilities.

References

Read the full report for CVE-2026-55874 on our website for more details including interactive diagrams and full exploit analysis.

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