SSRF allowlist bypass via percent-encoded host in hackney_CVE-2026-47076

6.9 / 10

MEDIUM

CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N

Description

Interpretation Conflict vulnerability in benoitc hackney allows Server Side Request Forgery. hackney_url:normalize/2 URL-decodes the host component after the URL has been parsed into a #hackney_url{} record. OTP's uri_string:parse/1 and inet:parse_address/1 do not decode percent-escapes in the host, so a URL such as http://%31%32%37%2E%30%2E%30%2E%31/ is seen by a caller's allowlist validator with host %31%32%37%2E%30%2E%30%2E%31 (not an IP address), which passes the allowlist check. hackney's normalizer then decodes the host to 127.0.0.1 and opens a TCP connection to loopback. Because hackney:request/5 always calls hackney_url:normalize/2 with no opt-out, every request that takes a binary or list URL is affected. The same technique reaches cloud instance metadata services (169.254.169.254), RFC1918 networks, and any admin interface listening on localhost.

This issue affects hackney: from 0.13.0 before 4.0.1.

Basic Information

ID CVE-2026-47076

Source EEF

Published May 25, 2026 at 14:00

Affected Product

Vendor benoitc

Product hackney

Version 0.13.0

Affected Versions benoitc hackney 0.13.0
benoitc hackney 4d725507588942fd00efca15b86da3273656510a

CWE Classification

CWE-436 CWE-918

References

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    "description": "Interpretation Conflict vulnerability in benoitc hackney allows Server Side Request Forgery. hackney_url:normalize/2 URL-decodes the host component after the URL has been parsed into a #hackney_url{} record. OTP's uri_string:parse/1 and inet:parse_address/1 do not decode percent-escapes in the host, so a URL such as http://%31%32%37%2E%30%2E%30%2E%31/ is seen by a caller's allowlist validator with host %31%32%37%2E%30%2E%30%2E%31 (not an IP address), which passes the allowlist check. hackney's normalizer then decodes the host to 127.0.0.1 and opens a TCP connection to loopback. Because hackney:request/5 always calls hackney_url:normalize/2 with no opt-out, every request that takes a binary or list URL is affected. The same technique reaches cloud instance metadata services (169.254.169.254), RFC1918 networks, and any admin interface listening on localhost.\n\nThis issue affects hackney: from 0.13.0 before 4.0.1.",
    "published": "2026-05-25T14:00:46.707Z",
    "modified": "2026-05-25T14:00:46.707Z",
    "type": "cve",
    "title": "SSRF allowlist bypass via percent-encoded host in hackney",
    "source": "EEF",
    "references": "https://github.com/benoitc/hackney/security/advisories/GHSA-pj7v-xfvx-wmjq\nhttps://cna.erlef.org/cves/CVE-2026-47076.html\nhttps://osv.dev/vulnerability/EEF-CVE-2026-47076\nhttps://github.com/benoitc/hackney/commit/452620a92ec1da2e6b4862a049a2a4f04b42068f",
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