{"id":"EEF-CVE-2026-115700","summary":"SSRF allowlist bypass via percent-encoded bracketed IPv6 or trailing-dot IP literal in hackney","details":"## Summary\n\nInterpretation Conflict vulnerability in `hackney_url` in benoitc hackney allows Server Side Request Forgery via a percent-encoded bracketed IPv6 literal or an IP literal with a trailing dot. A host such as `%5B%3A%3Affff%3A127%2E0%2E0%2E1%5D` (decoding to `[::ffff:127.0.0.1]`) or `127.0.0.1.` is not an IP address to a caller's allowlist built on `uri_string:parse/1` and `inet:parse_address/1`, while hackney connects to the address it denotes. The same applies to a `Location` target when redirects are followed.\n\nThe IP-literal gate that `hackney_url:normalize/2` applies to a percent-decoded host, added to close the percent-encoded IP bypass of CVE-2026-47076, passes the decoded value to `inet_parse:address/1` as is. The connect path in `hackney_happy:parse_address/1` drops a surrounding bracket pair, and the resolver ignores a trailing dot, so both forms pass the gate and still reach the literal address. Domain names with a trailing dot and unencoded IPv6 literals are not affected.\n\nThis issue affects hackney: from 4.0.1 before 4.9.0.\n\n## Details\n\n**1. The gate.** `hackney_url:normalize/2` in `src/hackney_url.erl` percent-decodes a host that is not already an IP literal and raises `invalid_url_host` when `inet_parse:address/1` accepts the decoded value. This closed the plain percent-encoded IP case.\n\n**2. What the connect path accepts.** `hackney_happy:parse_address/1` removes a surrounding `[...]` pair before calling `inet:parse_address/1`, and the resolver treats a trailing dot as the root label. Neither form is accepted by `inet_parse:address/1`, so `[::ffff:127.0.0.1]` and `127.0.0.1.` pass the gate.\n\n**3. Result.** A percent-encoded bracketed IPv6 literal such as `%5B%3A%3Affff%3A127%2E0%2E0%2E1%5D`, or an IPv4 literal with a trailing dot, is not an IP address to a caller's check based on `uri_string:parse/1` and `inet:parse_address/1`, but hackney connects to the address it denotes. The same applies to a `Location` target when redirects are followed. The fix strips one bracket pair and one trailing dot in `ip_candidate/1` before the gate.\n\n## Impact\n\nAn application that checks user-supplied URLs against an IP allowlist before handing them to hackney can be made to request loopback, link-local metadata and private-network addresses that the allowlist rejects when they are written plainly.\n\n## Workarounds\n\nRun the allowlist on the host that `hackney_url:normalize/1` returns for the parsed URL, and strip a surrounding bracket pair and a trailing dot from it before the IP check, so the check sees the same address the connect path uses.\n\n## Configurations\n\nThe application passes URLs that an untrusted party can influence to hackney and relies on its own host allowlist, built on `uri_string:parse/1` or `inet:parse_address/1`, to keep requests away from internal addresses.","aliases":["CVE-2026-115700"],"modified":"2026-10-26T14:00:04.842678043Z","published":"2026-10-26T13:49:02.744Z","database_specific":{"capec_ids":["CAPEC-664"],"cpe_ids":["cpe:2.3:a:benoitc:hackney:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-436","CWE-918"]},"references":[{"type":"ADVISORY","url":"https://github.com/benoitc/hackney/releases/tag/4.9.0"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-115700.html"},{"type":"WEB","url":"https://github.com/benoitc/hackney/pull/987"},{"type":"WEB","url":"https://github.com/benoitc/hackney/commit/452620a92ec1da2e6b4862a049a2a4f04b42068f"},{"type":"FIX","url":"https://github.com/benoitc/hackney/commit/f19561a0b422376348c91537e51377ab7325f4ee"},{"type":"PACKAGE","url":"https://hex.pm/packages/hackney"}],"affected":[{"package":{"name":"hackney","ecosystem":"Hex","purl":"pkg:hex/hackney"},"ranges":[{"type":"SEMVER","events":[{"introduced":"4.0.1"},{"fixed":"4.9.0"}]}],"versions":["4.0.1","4.0.2","4.0.3","4.1.0","4.2.0","4.2.1","4.2.2","4.2.3","4.3.0","4.4.0","4.4.1","4.4.2","4.4.3","4.4.5","4.5.0","4.5.1","4.5.2","4.6.0","4.6.1","4.7.0","4.7.1","4.7.2","4.7.3","4.7.4","4.8.0","4.8.1","4.8.2","4.8.3","4.8.4","4.8.5","4.8.6","4.8.7"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-115700.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/benoitc/hackney","events":[{"introduced":"452620a92ec1da2e6b4862a049a2a4f04b42068f"},{"fixed":"f19561a0b422376348c91537e51377ab7325f4ee"}]}],"versions":["4.8.7","4.8.6","4.8.5","4.8.4","4.8.3","4.8.2","4.8.1","4.8.0","4.7.4","4.7.3","4.7.2","4.7.1","4.7.0","4.6.1","4.6.0","4.5.2","4.5.1","4.5.0","4.4.5","4.4.4","4.4.3","4.4.2","4.4.1","4.4.0","4.3.0","4.2.3","4.2.2","4.2.1","4.2.0","4.1.0","4.0.3","4.0.2","4.0.1"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-115700.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","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"}],"credits":[{"name":"Eurico Nicacio","type":"FINDER"},{"name":"Eurico Nicacio","type":"REPORTER"},{"name":"Benoit Chesneau","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"COORDINATOR"}]}