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EUVD-2026-322100

fkie_cve-2026-47076

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.

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

Affected: Hex: hackney

### 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:

```erlang 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 refl…