GHSA-9653-rcfr-5c62
Fix: benoitc/hackney@31f6f0eGHSA-9653-rcfr-5c62 is a CWE-770 vulnerability in hackney. O3 Security confirms whether GHSA-9653-rcfr-5c62 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Hackney vulnerable to atom-table exhaustion via unrecognized URL schemes
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 GHSA-9653-rcfr-5c62.
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
CVE-2026-47067 is an atom table exhaustion vulnerability (CWE-770) in hackney's URL parser (src/hackney_url.erl). hackney_url:parse_url/1 converts every URL scheme it encounters into a BEAM atom via binary_to_atom/2. Because BEAM atoms are never garbage-collected and the atom table has a hard limit of 1,048,576 entries, an attacker who can feed URLs with attacker-chosen scheme prefixes — directly as request targets, as webhook/callback URLs, or via Location headers in redirect chains — can exhaust the atom table and crash the entire BEAM VM with system_limit.
Details
1. Scheme extraction and conversion
In src/hackney_url.erl, parse_url/1 extracts the scheme binary (the part before ://), validates it with is_valid_scheme/1 (RFC 3986 alphabet: alpha-led, <=19 bytes, alphanumeric/+/-/. body), lowercases it, then calls:
binary_to_atom(SchemeLower, utf8)
The resulting atom is stored on the #hackney_url{} record and returned to the caller.
2. Permanent atom accumulation
The validation constrains the alphabet but not uniqueness. The allowed scheme space is enormous (≈52·65¹⁸ values), far exceeding the default atom limit of 1,048,576. Each distinct scheme mints a new permanent atom. Even when hackney subsequently rejects an unsupported scheme with {error, {unsupported_scheme, _}}, the atom has already been interned and is never reclaimed.
3. Crash vector
The most dangerous path is redirect following: when hackney follows a Location header, the redirect target URL is re-parsed by the same function. An attacker-controlled server can serve a sequence of redirects — or a batch of URLs from an upstream feed — each with a fresh unique scheme, driving the atom count monotonically upward. At the limit the BEAM emits system_limit and the node terminates; recovery requires a full restart.
PoC
- Call
hackney_url:parse_url/1(or:hackney.request/5) repeatedly with URLs whose scheme prefixes are unique on each call:aaaa://x,aaab://x,aaac://x, … - After enough iterations, observe
erlang:system_info(:atom_count)climbing by one per unique scheme. - At 1,048,576 atoms the VM crashes with
system_limit.
Alternatively, point hackney at a server that replies with a feed of ~1M URLs with distinct schemes (or uses redirect chains with rotating schemes); the atom table is exhausted and the node crashes without the client being able to intervene.
Impact
Unauthenticated remote denial of service via permanent resource exhaustion leading to VM termination. Any application using hackney 2.0.0 through 4.0.0 that processes attacker-influenced URLs — direct request targets, webhook URLs, or Location headers in followed redirects — is affected. No authentication or special configuration is required. CVSS v4.0 score: 8.7 (HIGH).
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💧Hex | hackney | ≥ 2.0.0&&< 4.0.1 | 4.0.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hackney. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update hackney to 4.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-9653-rcfr-5c62 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 pinpoints whether GHSA-9653-rcfr-5c62 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-9653-rcfr-5c62. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-9653-rcfr-5c62 in your dependencies?
O3 detects GHSA-9653-rcfr-5c62 across Hex dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.