CVE-2026-47073 Unbounded memory consumption in WebSocket client in hackney
A malicious WebSocket server can cause unbounded memory consumption in the hackney client, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-47073?
CVE-2026-47073 is a high-severity denial of service 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
Allocation of Resources Without Limits or Throttling vulnerability in benoitc hackney allows Flooding. The WebSocket client in src/hackney_ws.erl imposes no upper bound on memory consumption in three code paths. First, read_handshake_response/3 accumulates received bytes into a growing buffer with no size cap; the per-receive timeout resets on every chunk, so a server that streams bytes without ever sending \r\n\r\n causes the buffer to grow until memory is exhausted. Second, parse_payload/9 and parse_active_payload/8 do not validate the declared frame payload length against any limit; because RFC 6455 allows payload lengths up to 2^63-1 bytes, a server that announces a very large frame and dribbles bytes causes the accumulation buffer to grow until OOM. Third, the frag_buffer field in #ws_data{} accumulates continuation frames indefinitely; a server that sends an endless stream of non-final (nofin) fragmented frames without ever sending a final (fin) frame grows frag_buffer without bound.
In all three cases the attacker only needs to control the WebSocket server the hackney client connects to, with no authentication or special client configuration required.
This issue affects hackney: from 2.0.0 before 4.0.1.
Weakness: CWE-400
Which versions are affected by CVE-2026-47073?
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-2026-47073?
Upgrade hackney to 4.0.1 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-47073 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-47073 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-2026-47071 SOCKS5 TLS upgrade ignores caller timeout in hackney
- CVE-2026-47077 Unbounded body accumulation in HTTP/3 response loop in hackney
- CVE-2026-47072 CRLF injection in WebSocket upgrade request in hackney
Sources
Also known as EEF-CVE-2026-47073, GHSA-q8jg-fgj4-fphf.