A flaw was found in SwiftNIO HTTP/2. This vulnerability allows a remote attacker to perform HTTP request smuggling or response splitting. The issue stems from insufficient validation of incoming HTTP/2 HEADERS frames, which are parts of an HTTP/2 request. This allows special control characters, such as carriage return (CR) and line feed (LF), to reach an HTTP/1.1 backend, potentially bypassing security controls and enabling malicious manipulation of web requests or responses.

SwiftNIO HTTP/2 was missing validation on inbound HEADERS frames that let CR, LF, NUL, SP and other control characters reach an HTTP/1.1 backend through NIOHTTP2's HTTP/2-to-HTTP/1 codec, enabling HTTP request smuggling or response splitting. This vulnerability is addressed in swift-nio-http2 version 1.45.0.

swift-nio-http2: Missing CR/LF/NUL validation in header values