CVE-2026-21862
RustFS has SourceIp bypass via spoofed X-Forwarded-For/Real-IP headers
Description
### 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](https://github.com/user-attachments/files/24038162/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.
How to fix CVE-2026-21862
To remediate CVE-2026-21862, upgrade the affected package to a fixed version below.