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

Vulnerability summary

CVE-2026-47072 is a high (CVSS 7.5) vulnerability in benoitc hackney. EPSS estimates a 0.54% chance of exploitation in the next 30 days, higher than 45.6% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 25-05-2026
   PublishedVulnerability first disclosed.
2. 27-05-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-93Improper Neutralization of CRLF SequencesThe product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.