Summary
Mint's HTTP/1 request encoder splices the caller-supplied method and target directly into the request line without character validation. An application that forwards attacker-controlled input as the HTTP method or the target to Mint.HTTP.request/5 is exposed to request-line CRLF injection, allowing the attacker to terminate the request line early, inject arbitrary headers, and pipeline a fully attacker-chosen second request onto the same TCP connection.
Details
encode_request_line/2 in lib/mint/http1/request.ex writes method and target to the wire verbatim. encode_headers/1 validates header names and values, but there is no equivalent validate_method!/1.
Mint 1.7.0 added validate_request_target/2, which rejects CRLF and other control characters in target by default and closes the path/query vector. The method field remains unvalidated, so a CRLF-bearing method such as "GET / HTTP/1.1\r\nX-Smuggled: 1\r\nGET /admin" is accepted and written to the socket as-is. Bytes after the first \r\n are interpreted by the peer as an injected header, or, with a second \r\n, as an additional pipelined request.
PoC
- Stand up a Mint-using gateway/proxy that calls
Mint.HTTP.request(conn, method, "/", [], nil) with method taken from caller input.
- Send a request whose forwarded method is
"GET / HTTP/1.1\r\nX-Smuggled-Header: pwned\r\nGET /admin/delete-everything".
- Observe the bytes received by the upstream server: the smuggled header line and the second request line appear verbatim in the outbound stream.
Impact
CRLF injection / HTTP request smuggling in the HTTP/1 client encoder, exploitable under default configuration whenever an application passes caller-influenced input as the HTTP method. An attacker who controls the method can inject arbitrary outbound headers (forged Host, Authorization, cache-poisoning headers) and smuggle additional, fully attacker-chosen requests to the upstream server over the same connection, potentially reaching endpoints the legitimate caller never intended to invoke.
Resources
References
Summary
Mint's HTTP/1 request encoder splices the caller-supplied
methodandtargetdirectly into the request line without character validation. An application that forwards attacker-controlled input as the HTTP method or the target toMint.HTTP.request/5is exposed to request-line CRLF injection, allowing the attacker to terminate the request line early, inject arbitrary headers, and pipeline a fully attacker-chosen second request onto the same TCP connection.Details
encode_request_line/2inlib/mint/http1/request.exwritesmethodandtargetto the wire verbatim.encode_headers/1validates header names and values, but there is no equivalentvalidate_method!/1.Mint 1.7.0 added
validate_request_target/2, which rejects CRLF and other control characters intargetby default and closes the path/query vector. Themethodfield remains unvalidated, so a CRLF-bearing method such as"GET / HTTP/1.1\r\nX-Smuggled: 1\r\nGET /admin"is accepted and written to the socket as-is. Bytes after the first\r\nare interpreted by the peer as an injected header, or, with a second\r\n, as an additional pipelined request.PoC
Mint.HTTP.request(conn, method, "/", [], nil)withmethodtaken from caller input."GET / HTTP/1.1\r\nX-Smuggled-Header: pwned\r\nGET /admin/delete-everything".Impact
CRLF injection / HTTP request smuggling in the HTTP/1 client encoder, exploitable under default configuration whenever an application passes caller-influenced input as the HTTP method. An attacker who controls the method can inject arbitrary outbound headers (forged
Host,Authorization, cache-poisoning headers) and smuggle additional, fully attacker-chosen requests to the upstream server over the same connection, potentially reaching endpoints the legitimate caller never intended to invoke.Resources
References