CVE-2026-47072

### Summary CRLF injection in hackney's WebSocket upgrade request builder (`src/hackney_ws.erl`). `init/1` copies the `host`, `path`, `headers`, and `protocols` options from the caller-supplied opts map verbatim into `#ws_data{}`, and `do_handshake/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 `do_handshake/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 `:hackney_ws.start_link/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

## Summary Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in benoitc hackney allows HTTP Request/Response Splitting. The WebSocket upgrade code in src/hackney\_ws.erl copies the host, path, headers (ExtraHeaders), and protocols options from the caller-supplied opts map into the internal #ws\_data{} record in init/1 and then splices them verbatim into the raw HTTP/1.1 upgrade request by binary concatenation in do\_handshake/1. No CRLF or NUL stripping is performed at any of these four injection sites. An attacker who controls any of these options — for example by forwarding URL components or header values from untrusted input into hackney\_ws:start\_link/1 — can inject arbitrary HTTP headers into the outbound WebSocket upgrade request, leading to header injection, credential spoofing toward the upstream server, log and cache poisoning, or request smuggling via intermediary proxies. This issue affects hackney: from 2.0.0 before 4.0.1.