Ceph RGW

10 Non-Obvious S3 Integration Vulnerabilities Exposed in Web Application Bug Bounty Research

Security researcher Sergey Bobrov, known as BlackFan, published a detailed analysis of S3 misconfigurations when integrated into web applications via proxies such as nginx. The article examines ten laboratory setups demonstrating issues ranging from stored XSS and bucket takeover to rewrite rule bypasses and cache poisoning. Key findings highlight how nginx path normalization differences, missing trailing slashes, and variable usage like $uri enable attackers to reach arbitrary buckets or inject HTTP request splitting payloads. The research covers both direct S3 client usage and proxy-based integrations, emphasizing ACL and Bucket Policy errors that expose data to any authenticated S3 user worldwide. Practical demonstrations include exploitation of Ceph RGW path traversal with ../ sequences and cache key collisions via response-content-type parameters. The work provides fingerprinting tables for identifying S3-compatible systems including MinIO, Ceph RGW, and Yandex Cloud based on headers and error responses.