CVE-2026-47073 — hackney
Fix: benoitc/hackney@ce0109eCVE-2026-47073 is a Uncontrolled Resource Consumption vulnerability in hackney. A fix is available for hackney — see the affected versions and patch details below.
Unbounded memory consumption in WebSocket client in hackney
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-47073.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
hackneyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Hex packages — download data is not available via public APIs for these ecosystems.
Description
Summary
The WebSocket client in src/hackney_ws.erl imposes no upper bound on memory consumption across three distinct code paths. In each case, an attacker-controlled WebSocket server can exhaust the connecting process's memory without any authentication or special client configuration.
Details
1. Handshake response buffer (read_handshake_response/3)
The function accumulates received bytes into a growing buffer waiting for \r\n\r\n. The per-receive timeout resets on every chunk, so a server that trickles bytes indefinitely without completing the HTTP upgrade response grows the buffer until OOM. No total-size cap exists.
2. Frame payload accumulation (parse_payload/9, parse_active_payload/8)
parse_payload/9 (lines 816–817 and 825–826) appends each received chunk into a Buffer binary via <<Buffer/binary, MoreData/binary>> whenever the frame parser returns {more, ...}. parse_active_payload/8 does the same in active mode by appending each incoming tcp/ssl message to #ws_data.buffer. RFC 6455 permits payload lengths up to 2⁶³-1 bytes, and neither path validates the declared Len against any limit. The recv_timeout applies per chunk, not to the whole frame, so a slow trickle never triggers it.
3. Fragmentation buffer (frag_buffer)
The frag_buffer field of #ws_data{} accumulates continuation frames. A server that sends an unbounded stream of non-final (nofin) fragments without ever sending a final (fin) frame grows frag_buffer without bound.
PoC
- Stand up a WebSocket server and connect to it with hackney's WebSocket client.
- Trigger any of the three paths: (a) never send
\r\n\r\nduring the handshake; (b) announce a very large frame payload and dribble bytes slowly; (c) send an endless stream ofnofincontinuation frames. - Observe the hackney process's memory growing until the BEAM OOM-kills it or the node crashes.
Impact
Denial of service via unbounded memory consumption. Affects hackney 2.0.0 through 4.0.0 for any application using the WebSocket client against an attacker-controlled server. No authentication or special configuration is required on the client side. CVSS v4.0: 8.7 (HIGH).
Resources
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💧Hex | hackney | ≥ 2.0.0&&< 4.0.1 | 4.0.1mix deps.update hackney |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hackney, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hackney to 4.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-47073 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-47073 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-47073. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-47073 in your dependencies?
O3 Security finds CVE-2026-47073 across Hex dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.