{"id":"EEF-CVE-2026-115693","summary":"Custom cacerts or cacertfile do not restrict trust to the pinned CA in hackney","details":"## Summary\n\nImproper Certificate Validation vulnerability in `hackney_ssl` in benoitc hackney allows an on-path attacker to impersonate a server pinned to a private certificate authority via a certificate chain that ends in a publicly trusted root. hackney adds `{partial_chain, fun hackney_ssl:partial_chain/1}` to every `verify_peer` configuration. The callback returns any certificate in the peer chain whose public key matches a root in the bundled certifi store as the trust anchor, and OTP honours that callback over the configured `cacerts`. `hackney_ssl:merge_ssl_opts/3` kept the callback when the caller replaced the trust store with `cacerts` or `cacertfile` in `ssl_options`, so a connection pinned to a private CA still accepted any chain that carried a publicly trusted root.\n\nThe hostname check still applies, so the attacker needs a publicly trusted certificate for the pinned hostname.\n\nThis issue affects hackney: from 1.24.0 before 4.9.0.\n\n## Details\n\n**1. Default trust options.** `hackney_ssl:check_hostname_opts/1` builds the `verify_peer` options for every TLS connection: the certifi `cacerts`, a hostname `verify_fun`, and `{partial_chain, fun hackney_ssl:partial_chain/1}`. The callback walks the peer chain and returns `{trusted_ca, Cert}` for the first certificate whose public key matches a root in the bundled certifi store, which lets OTP accept chains that end in a cross-signed root.\n\n**2. Merge keeps the callback.** When the caller passes `ssl_options`, `hackney_ssl:merge_ssl_opts/3` merges them over the defaults with the caller's values winning per key. `cacerts` or `cacertfile` replace the trust store, and a `cacertfile` removes the default `cacerts`, but `partial_chain` has no counterpart in the caller's options and stays.\n\n**3. Validation.** OTP consults `partial_chain` before the configured trust store. A peer chain that carries any publicly trusted root therefore gets that root as its trust anchor, and the pinned `cacerts` are never consulted. Only the hostname `verify_fun` still constrains the attacker.\n\n## Impact\n\nAn attacker positioned between the client and a server pinned to a private CA, holding a publicly trusted certificate for the pinned hostname, can impersonate the server and read or modify the traffic the client sends and receives.\n\n## Workarounds\n\nPass your own `{partial_chain, Fun}` in `ssl_options` alongside `cacerts` or `cacertfile`. A caller-supplied `partial_chain` replaces hackney's in the merge, and a callback that returns `unknown_ca` makes OTP validate against the configured `cacerts` only.\n\n## Configurations\n\nThe caller passes `cacerts` or `cacertfile` in `ssl_options` to restrict trust to a private CA, without a `partial_chain` of its own. Connections that use hackney's default certifi trust store are not affected.","aliases":["CVE-2026-115693"],"modified":"2026-10-26T14:00:04.842588289Z","published":"2026-10-26T13:49:29.374Z","database_specific":{"cpe_ids":["cpe:2.3:a:benoitc:hackney:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-295"],"capec_ids":["CAPEC-94"]},"references":[{"type":"WEB","url":"https://github.com/benoitc/hackney/pull/978"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-115693.html"},{"type":"ADVISORY","url":"https://github.com/benoitc/hackney/releases/tag/4.9.0"},{"type":"WEB","url":"https://github.com/benoitc/hackney/commit/d8a9afcf5c3849904274e2eba1df56c63d1a1a0c"},{"type":"FIX","url":"https://github.com/benoitc/hackney/commit/915eb5737e9c489d8fc22eec8cdae30e9b027be4"},{"type":"PACKAGE","url":"https://hex.pm/packages/hackney"}],"affected":[{"package":{"name":"hackney","ecosystem":"Hex","purl":"pkg:hex/hackney"},"ranges":[{"type":"SEMVER","events":[{"introduced":"1.24.0"},{"fixed":"4.9.0"}]}],"versions":["1.24.0","1.24.1","1.25.0","2.0.0","2.0.0-beta.1","2.0.1","3.0.0","3.0.1","3.0.2","3.0.3","3.1.0","3.1.1","3.1.2","3.2.0","3.2.1","4.0.0","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-2026-115693.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/benoitc/hackney","events":[{"introduced":"d8a9afcf5c3849904274e2eba1df56c63d1a1a0c"},{"fixed":"915eb5737e9c489d8fc22eec8cdae30e9b027be4"}]}],"versions":["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","4.0.0","3.2.1","3.2.0","3.1.2","3.1.1","3.1.0","3.0.3","3.0.2","3.0.1","2.0.1","2.0.0","2.0.0-beta.1","1.25.0","1.24.1","1.24.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-115693.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"}],"credits":[{"name":"Martin Karrer","type":"FINDER"},{"name":"Martin Karrer","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"COORDINATOR"}]}