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Hackney has SSRF allowlist bypass in hackney_url:normalize/2 via percent-encoded hostGHSA-pj7v-xfvx-wmjq

Fix: benoitc/hackney@452620a

GHSA-pj7v-xfvx-wmjq is a CWE-436 vulnerability in hackney. A fix is available for hackney — see the affected versions and patch details below.

Also known asCVE-2026-47076EEF-CVE-2026-47076
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 25, 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.

Exploitation and automatability from CISA’s SSVC triage for GHSA-pj7v-xfvx-wmjq.

EPSS Exploitation Probability

via FIRST.org ↗
0.2%probability of exploitation in next 30 days
Lower Risk+0.07%
Lower risk than most CVEs14th percentile — riskier than 14% of all scored CVEsHighest risk
0.00%0.24%0.49%0.73%0.0%0.2%Jun 26Sep 26Oct 26

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

hackney_url:normalize/2 URL-decodes the host component of a parsed URL, but the caller's SSRF allowlist runs before normalization using OTP's uri_string:parse/1 and inet:parse_address/1, neither of which decodes percent-escapes in hostnames. A URL like http://%31%32%37%2E%30%2E%30%2E%31/ presents an encoded, non-IP-looking host to the validator, which passes the allowlist check; hackney's normalizer then decodes it to 127.0.0.1 and connects to loopback. Because hackney:request/5 always calls normalize/2 with no opt-out, every request path that accepts a binary or list URL is affected. This is a parser-differential SSRF in the same class as CVE-2025-1211, but in a different function.

Details

In src/hackney_url.erl (lines 161–186), normalize/2 checks whether the parsed host is already a dotted-quad or IPv6 literal via inet_parse:address/1. Percent-encoded forms like %31%32%37%2E%30%2E%30%2E%31 fail that check and fall into the catch-all branch, where urldecode/1 decodes the host before passing it to IDNA conversion:

Host1 = binary_to_list(
           urldecode(unicode:characters_to_binary(Host0))
         ),

The decoded host ("127.0.0.1") replaces the original in the returned #hackney_url{} record. hackney:request/5 at src/hackney.erl:463 always calls normalize/2, so the decoded host is what do_dispatch/1 and add_host_header/2 ultimately use. The on-wire Host: header and the TCP connect target both reflect the decoded value.

The same payload pattern reaches the AWS/GCP/Azure IMDS (169.254.169.254), RFC1918 ranges, and any localhost admin endpoint. The 1.21.0 patch for CVE-2025-1211 fixed a separate differential in parse_url/1 and did not touch normalize/2.

PoC

  1. Validate the URL with the canonical Erlang SSRF allowlist: uri_string:parse/1 returns host <<"%31%32%37%2E%30%2E%30%2E%31">>, inet:parse_address/1 returns {error, einval}, so the allowlist accepts it.
  2. Pass the same URL to hackney:get/1.
  3. hackney's normalize/2 decodes the host to "127.0.0.1" and connects to 127.0.0.1:80. The internal service receives the request with Host: 127.0.0.1.

Impact

Unauthenticated SSRF bypassing the canonical Erlang allowlist pattern. Affects hackney 0.13.0 through 4.0.0 for any application that accepts attacker-supplied URLs. Targets include cloud IMDS endpoints, localhost admin interfaces, and RFC1918 backends. CVSS v4.0: 6.9 (MEDIUM).

Resources

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
💧Hexhackney≥ 0.13.0&&< 4.0.14.0.1mix deps.update hackney

Affected Products

1 product · 1 configurations
Application
hackneybenoitc
≥ 0.13.0 && < 4.0.1
range

Detection & mitigation playbook

Open-source dependency

  1. 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.

  2. Fix

    Update hackney to 4.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-pj7v-xfvx-wmjq is resolved across your whole dependency graph.

  3. Workarounds

    Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.

Frequently Asked Questions

### Summary `hackney_url:normalize/2` URL-decodes the host component of a parsed URL, but the caller's SSRF allowlist runs before normalization using OTP's `uri_string:parse/1` and `inet:parse_address/1`, neither of which decodes percent-escapes in hostnames. A URL like `http://%31%32%37%2E%30%2E%30%2E%31/` presents an encoded, non-IP-looking host to the validator, which passes the allowlist check; hackney's normalizer then decodes it to `127.0.0.1` and connects to loopback. Because `hackney:request/5` always calls `normalize/2` with no opt-out, every request path that accepts a binary or lis
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