CVE-2026-47072: CRLF injection in WebSocket upgrade request in hackney

Summary

CRLF injection in hackney's WebSocket upgrade request builder (src/hackneyws.erl). init/1 copies the host, path, headers, and protocols options from the caller-supplied opts map verbatim into #wsdata{}, and dohandshake/1 splices them directly into the raw HTTP/1.1 upgrade request by binary concatenation with no \r\n or \0 stripping. A caller that passes any of these fields from untrusted input can inject arbitrary header lines into the outbound upgrade request.

Details

dohandshake/1 builds the upgrade request at several concatenation sites:

- Host header (lines 583–590): the host binary is written straight into Host: <host>:<port>\r\n. - Sec-WebSocket-Protocol (lines 601–602): protocol tokens are joined with , and appended as a header line. - Extra headers (line 606): caller-supplied {Name, Value} tuples are concatenated as Name: Value\r\n with no sanitization of either component. - Request path (line 611): the path is interpolated into the GET <path> HTTP/1.1\r\n request line.

None of these sites reject \r, \n, or \0. A header value like <<"benign\r\nAuthorization: Bearer token">> produces two distinct header lines on the wire. A path with an embedded \r\n rewrites the request line itself.

PoC

1. Call :hackneyws.startlink/1 with headers: [{"X-User", "v\r\nAuthorization: Bearer attacker"}]. 2. Connect to a raw TCP listener and capture the bytes hackney writes. 3. The request contains a standalone Authorization: Bearer attacker line that the upstream WebSocket server parses as a legitimate header.

Impact

Header injection / request smuggling in outbound WebSocket upgrades. Affects hackney 2.0.0 through 4.0.0 wherever host, path, headers, or protocols options are populated from network or user input. Consequences include forging authentication headers toward the upstream server, log and cache poisoning, and request smuggling through intermediary proxies. CVSS v4.0: 6.9 (MEDIUM).

Resources

Introduction commit: https://github.com/benoitc/hackney/commit/690cecaf236fba49526da404a5bc889a24367a3e Patch commit: https://github.com/benoitc/hackney/commit/52310ca807e7b48441ba0e9129171f535313fdd1