CVE-2026-47072 CRLF injection in WebSocket upgrade request in hackney
Attackers can inject CRLF sequences into WebSocket upgrade requests via untrusted input, enabling header injection and request smuggling in applications using hackney.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-47072?
CVE-2026-47072 is a medium-severity vulnerability in benoitc hackney, published on 25 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-93
Which versions are affected by CVE-2026-47072?
3 open source packages ship an affected version, including hackney. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
hackney Hex | From 2.0.0 | 4.0.1 |
hackney Hex | From 2.0.0 | 4.0.1 |
hackney Hex | From 2.0.0 | 4.0.1 |
Products include Benoitc Hackney.
How do I fix CVE-2026-47072?
Upgrade hackney to 4.0.1 or later.
Is CVE-2026-47072 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-47072 exists.
Other vulnerabilities in benoitc hackney
- CVE-2026-47066 Infinite loop in Alt-Svc header parser in hackney
- CVE-2026-47067 Atom table exhaustion via unrecognized URL schemes in hackney
- CVE-2026-47073 Unbounded memory consumption in WebSocket client in hackney
- CVE-2026-47071 SOCKS5 TLS upgrade ignores caller timeout in hackney
- CVE-2026-47077 Unbounded body accumulation in HTTP/3 response loop in hackney
Sources
Also known as EEF-CVE-2026-47072, GHSA-f9vr-g2g2-x9fg.