GHSA-PJ7V-XFVX-WMJQ
Vulnerability from github – Published: 2026-06-26 21:54 – Updated: 2026-06-26 21:54Summary
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
- Validate the URL with the canonical Erlang SSRF allowlist:
uri_string:parse/1returns host<<"%31%32%37%2E%30%2E%30%2E%31">>,inet:parse_address/1returns{error, einval}, so the allowlist accepts it. - Pass the same URL to
hackney:get/1. - hackney's
normalize/2decodes the host to"127.0.0.1"and connects to127.0.0.1:80. The internal service receives the request withHost: 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
- Introduction commit: https://github.com/benoitc/hackney/commit/4d725507588942fd00efca15b86da3273656510a
- Patch commit: https://github.com/benoitc/hackney/commit/452620a92ec1da2e6b4862a049a2a4f04b42068f
{
"affected": [
{
"package": {
"ecosystem": "Hex",
"name": "hackney"
},
"ranges": [
{
"events": [
{
"introduced": "0.13.0"
},
{
"fixed": "4.0.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-47076"
],
"database_specific": {
"cwe_ids": [
"CWE-436",
"CWE-918"
],
"github_reviewed": true,
"github_reviewed_at": "2026-06-26T21:54:55Z",
"nvd_published_at": "2026-05-25T15:16:22Z",
"severity": "MODERATE"
},
"details": "### Summary\n\n`hackney_url:normalize/2` URL-decodes the host component of a parsed URL, but the caller\u0027s SSRF allowlist runs before normalization using OTP\u0027s `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\u0027s 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.\n\n### Details\n\nIn `src/hackney_url.erl` (lines 161\u2013186), `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:\n\n```erlang\nHost1 = binary_to_list(\n urldecode(unicode:characters_to_binary(Host0))\n ),\n```\n\nThe 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.\n\nThe 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`.\n\n### PoC\n\n1. Validate the URL with the canonical Erlang SSRF allowlist: `uri_string:parse/1` returns host `\u003c\u003c\"%31%32%37%2E%30%2E%30%2E%31\"\u003e\u003e`, `inet:parse_address/1` returns `{error, einval}`, so the allowlist accepts it.\n2. Pass the same URL to `hackney:get/1`.\n3. hackney\u0027s `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`.\n\n### Impact\n\nUnauthenticated 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)**.\n\n## Resources\n\n* Introduction commit: https://github.com/benoitc/hackney/commit/4d725507588942fd00efca15b86da3273656510a\n* Patch commit: https://github.com/benoitc/hackney/commit/452620a92ec1da2e6b4862a049a2a4f04b42068f",
"id": "GHSA-pj7v-xfvx-wmjq",
"modified": "2026-06-26T21:54:55Z",
"published": "2026-06-26T21:54:55Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/benoitc/hackney/security/advisories/GHSA-pj7v-xfvx-wmjq"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-47076"
},
{
"type": "WEB",
"url": "https://github.com/benoitc/hackney/commit/452620a92ec1da2e6b4862a049a2a4f04b42068f"
},
{
"type": "WEB",
"url": "https://cna.erlef.org/cves/CVE-2026-47076.html"
},
{
"type": "PACKAGE",
"url": "https://github.com/benoitc/hackney"
},
{
"type": "WEB",
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-47076"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "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",
"type": "CVSS_V4"
}
],
"summary": "Hackney has SSRF allowlist bypass in hackney_url:normalize/2 via percent-encoded host"
}
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|---|
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