How severe is CVE-2026-47071?

No CVSS score has been assigned to CVE-2026-47071 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-47071?

CVE-2026-47071 affects the following packages: hackney (Hex). Ecosystems affected: Hex.

How do I fix CVE-2026-47071?

Update hackney to 4.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-47071 is resolved across your whole dependency graph.

How do I detect CVE-2026-47071 in my Hex dependencies?

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.

How do I mitigate CVE-2026-47071 if there is no patch (or I can't update yet)?

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.

Is CVE-2026-47071 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-47071 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-47071?

CVE-2026-47071 has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 53th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-47071?

CVE-2026-47071 is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-47071 published, and has it been updated?

CVE-2026-47071 was published on May 25, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💧 Hex

Not in CISA KEV

CVE-2026-47071 — hackney

Fix: benoitc/hackney@5ccdab7

CVE-2026-47071 is a Uncontrolled Resource Consumption vulnerability in hackney. A fix is available for hackney — see the affected versions and patch details below.

SOCKS5 TLS upgrade ignores caller timeout in hackney

Also known asEEF-CVE-2026-47071GHSA-gp9c-pm5m-5cxr

Published

May 25, 2026

Updated

Oct 21, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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-2026-47071.

EPSS Exploitation Probability

via FIRST.org ↗

0.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs53th percentile — riskier than 53% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

💧hackney

Real-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 SOCKS5 transport in src/hackney_socks5.erl correctly applies the caller-supplied timeout to the SOCKS5 negotiation phase, but then upgrades the tunnel to TLS using ssl:connect/2 (the two-argument form), which defaults to infinity. The Timeout value is in scope at that call site but is never forwarded. A hostile or man-in-the-middled SOCKS5 proxy that completes the SOCKS5 handshake normally and then stalls the TLS exchange will pin the connecting Erlang process and socket indefinitely, regardless of any connect_timeout or recv_timeout options the caller set.

Details

In src/hackney_socks5.erl, line 65, after the SOCKS5 negotiation succeeds, the code calls:

ssl:connect(Socket, SSLOpts)

The three-argument form ssl:connect/3 takes a timeout; the two-argument form used here defaults to infinity. The variable Timeout (already used for SOCKS5 recv calls earlier in the same function) is simply not passed. The bytes that drive the TLS handshake on the upstream side of the tunnel come from whatever endpoint the proxy connects to. A hostile proxy can complete SOCKS5 normally, then either stay silent or send a partial ServerHello and stop, keeping ssl:connect/2 blocked forever. No certificate forgery is needed.

PoC

Stand up a SOCKS5 proxy that completes the SOCKS5 greeting and CONNECT reply normally, then goes silent (never sends a TLS ServerHello).
Issue an HTTPS request through it via hackney with connect_timeout and recv_timeout set to a short value (e.g. 2000 ms).
Observe the calling process remains blocked well past the configured timeout, consuming a process and socket until killed externally.

Impact

Denial of service via unbounded process and socket consumption. Affects hackney 0.10.0 through 4.0.0 for any HTTPS request routed through a SOCKS5 proxy. The connect_timeout and recv_timeout options give a false sense of safety since they are not honored during the TLS upgrade. CVSS v4.0: 8.2 (HIGH).

Resources

Introduction commit: https://github.com/benoitc/hackney/commit/34cdbd1d20a282aacc286a89327465a3925b4c5d
Patch commit: https://github.com/benoitc/hackney/commit/5ccdab725c561a6f03d05a51f2d0664f98236dae

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
💧Hex	`hackney`	≥ 0.10.0&&< 4.0.1	4.0.1`mix deps.update hackney`

Affected Products

1 product · 1 configurations

Application

hackneybenoitc

≥ 0.10.0 && < 4.0.1

range

Detection & mitigation playbook

Open-source dependency

Detect
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-2026-47071 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.

Frequently Asked Questions

### Summary The SOCKS5 transport in `src/hackney_socks5.erl` correctly applies the caller-supplied timeout to the SOCKS5 negotiation phase, but then upgrades the tunnel to TLS using `ssl:connect/2` (the two-argument form), which defaults to `infinity`. The `Timeout` value is in scope at that call site but is never forwarded. A hostile or man-in-the-middled SOCKS5 proxy that completes the SOCKS5 handshake normally and then stalls the TLS exchange will pin the connecting Erlang process and socket indefinitely, regardless of any `connect_timeout` or `recv_timeout` options the caller set. ### De

O3 Security · Impact-Aware SCA

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