CVE-2026-126083

Action Pack is a framework for handling and responding to web requests. From 8.1 until 8.1.4.1, Since Rails 8.1.0, ActionDispatch::RemoteIp derives request.remote_ip from Rack::Request#forwarded_for, which under Rack 3 reads the RFC 7239 Forwarded header in preference to X-Forwarded-For. When a reverse proxy appends the client address to X-Forwarded-For but passes a client-supplied Forwarded header through unchanged, request.remote_ip returns an address chosen by the client, and the IP spoofing check does not raise, because it compares only Client-Ip with the forwarded addresses. An unauthenticated attacker could therefore spoof request.remote_ip, possibly bypassing IP-based access controls and rate limits keyed on the client address (including the default by: of rate_limit), and falsifying the client address in logs. An application is affected if it meets all of these requirements: Runs Rails 8.1.0 through 8.1.4 with Rack 3. Under Rack 2.2, forwarded_for reads only X-Forwarded-For. Is served behind a proxy that does not remove or overwrite a client-supplied Forwarded header. Relies on request.remote_ip for access control, rate limiting, or auditing. The fix detects a spoofed Forwarded header only when the proxy also sets X-Forwarded-For. An application whose proxy passes a client-supplied Forwarded header through and sets no X-Forwarded-For remains exposed after upgrading, and should configure the proxy to remove or overwrite Forwarded, or apply the workaround below. This issue is fixed in version 8.1.4.1.

• https://github.com/rails/rails/commit/2a01a5ac521184419d9a92fa2c25e102e68cd227
• https://github.com/rails/rails/releases/tag/v8.1.4.1
• https://github.com/rails/rails/security/advisories/GHSA-2gff-2mmg-m73p

• https://github.com/rails/rails/commit/2a01a5ac521184419d9a92fa2c25e102e68cd227
• https://github.com/rails/rails/releases/tag/v8.1.4.1
• https://github.com/rails/rails/security/advisories/GHSA-2gff-2mmg-m73p

• MEDIUMCVE-2026-100653PoC
• MEDIUMCVE-2026-101277
• MEDIUMCVE-2026-102275PoC
• MEDIUMCVE-2026-102630PoC
• MEDIUMCVE-2026-103592PoC
• LOWCVE-2026-105051PoC
• MEDIUMCVE-2026-107271PoC
• HIGHCVE-2026-107567

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