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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
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.