RustFS has SourceIp bypass via spoofed X-Forwarded-For/Real-IP headers

Summary

IP-based access control can be bypassed: get_condition_values trusts client-supplied X-Forwarded-For/X-Real-Ip without verifying a trusted proxy, so any reachable client can spoof aws:SourceIp and satisfy IP-allowlist policies.

Details

• Vulnerable code: rustfs/src/auth.rs:289-304 sets remote_addr from X-Forwarded-For/X-Real-Ip, then inserts SourceIp via get_source_ip_raw, with no trust boundary or proxy validation:
  • let remote_addr = header.get("x-forwarded-for").and_then(...).or_else(|| header.get("x-real-ip")...).unwrap_or("127.0.0.1");
  • args.insert("SourceIp", vec![get_source_ip_raw(header, remote_addr)]);
• This value feeds IAM/bucket policy evaluation in rustfs/src/storage/access.rs (authorization path), so any request that forges the header can meet aws:SourceIp conditions.
• No authentication is required beyond the request itself; the header is taken at face value even on direct connections.

PoC

rustfs-auth-trusted-ip-header-spoofing-poc.tar.gz

Steps (already included in rustfs-auth-trusted-ip-header-spoofing-poc/):

1. Start RustFS with two local volumes, e.g.:

     mkdir -p /tmp/rustfs-data1 /tmp/rustfs-data2
     RUSTFS_ACCESS_KEY=devadmin RUSTFS_SECRET_KEY=devadmin \
       cargo run --bin rustfs -- --address 0.0.0.0:9000 \
       /tmp/rustfs-data1 /tmp/rustfs-data2

2. From rustfs-auth-trusted-ip-header-spoofing-poc/, run:

     ENDPOINT=http://127.0.0.1:9000 make run

 The script:
  - Creates bucket `rustfs-trusted-ip-poc`.
  - Applies a bucket policy allowing `s3:ListBucket` only from `10.0.0.5/32` (`Principal: {"AWS":["*"]},` Resource array).
  - Sends three unauthenticated `ListBucket` calls:
      - Baseline (no spoof) → HTTP 403.
      - Spoofed `X-Forwarded-For: 10.0.0.5` → HTTP 200 (policy bypass).
      - Spoofed `X-Forwarded-For: 1.2.3.4` → HTTP 403.
  - Responses saved to `poc-baseline.xml`, `poc-spoofed.xml`, `poc-deny.xml`.

Impact

• Vulnerability type: Authorization bypass of IP-allowlist (aws:SourceIp) via header spoofing.
• Who is impacted: Any deployment relying on aws:SourceIp in IAM/bucket policies for S3 operations. Attackers with network reach to RustFS can forge forwarded-IP headers to gain list/read/write where IP restrictions were meant to block them.

Credits

Identified by SecMate (https://secmate.dev) automated analysis and validated during manual triage.