{"id":"CVE-2026-66883","summary":"Oidcc.Plug.Authorize user agent session binding inert due to case-sensitive header lookup","details":"Improper Handling of Case Sensitivity vulnerability in Erlang Ecosystem Foundation oidcc_plug (Oidcc.Plug.Authorize module) renders the user agent session binding inert, removing a defense in depth control against replay of a stolen session.\n\nThis vulnerability is associated with program files lib/oidcc/plug/authorize.ex and lib/oidcc/plug/authorization_callback.ex, and program routines Oidcc.Plug.Authorize.call/2 and Oidcc.Plug.AuthorizationCallback.call/2.\n\nOidcc.Plug.Authorize.call/2 reads the initiating client's user agent with get_req_header(conn, \"User-Agent\"). Plug lowercases incoming header names, but get_req_header/2 matches the supplied key exactly and performs no normalization of its own, so the mixed-case lookup always returns an empty list and nil is written into the session. On the callback side, Oidcc.Plug.AuthorizationCallback treats a stored nil user agent as nothing to compare and returns :ok without inspecting the request. The two behaviours combine so that the check passes unconditionally on every request, including for deployments that explicitly opted in with check_useragent: true, and an authorization callback can be completed from a different user agent than the one that initiated the flow without detection. The check fails open silently, with no error and no log entry, so a deployment cannot tell the binding is absent.\n\nThe impact is limited to defense in depth. The inert check does not by itself allow an attacker to complete an authorization flow; it removes one layer that would otherwise hinder use of a stolen or leaked session, such as an exfiltrated session cookie replayed from a different client. The CSRF/state, nonce, and PKCE checks are unaffected and continue to function. Deployments that never enabled check_useragent are not affected in practice, since they never expected the binding. The corresponding lookup in Oidcc.Plug.AuthorizationCallback correctly uses the lowercase key and is not affected.\n\nThis issue affects oidcc_plug: from 0.1.0-alpha.3 before 0.5.0.","aliases":["EEF-CVE-2026-66883","GHSA-w5r8-m75h-98fc"],"modified":"2026-08-06T03:48:34.469789039Z","published":"2026-08-04T11:46:05.191Z","database_specific":{"cna_assigner":"EEF","cwe_ids":["CWE-178"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66883.json","unresolved_ranges":[{"extracted_events":[{"introduced":"0a75fb139d8e2686d1b75e0d48962323d2181673"},{"fixed":"f15e52c5750aaba701104b10ed96cfac063bd557"}],"source":"AFFECTED_FIELD"}]},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-66883.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-66883"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66883.json"},{"type":"ADVISORY","url":"https://github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-66883"},{"type":"FIX","url":"https://github.com/erlef/oidcc_plug/commit/f15e52c5750aaba701104b10ed96cfac063bd557"},{"type":"PACKAGE","url":"https://github.com/erlef/oidcc_plug"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/erlef/oidcc_plug","events":[{"introduced":"66259d66202f7b1a5bfa5a04010fe95ef1631431"},{"fixed":"133995c0114ff610a738020ddfdb6d2adf69e81c"},{"fixed":"f15e52c5750aaba701104b10ed96cfac063bd557"}],"database_specific":{"source":["DESCRIPTION","REFERENCES"],"extracted_events":[{"introduced":"0.1.0-alpha.3"},{"fixed":"0.5.0"}]}}],"versions":["v0.4.0","v0.3.2","v0.3.1","v0.3.0","v0.2.2","v0.2.1","v0.2.0","v0.2.0-beta.1","v0.1.2","v0.1.1","v0.1.0","v0.1.0-rc.2","v0.1.0-rc.1","v0.1.0-alpha.4","v0.1.0-alpha.3"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-66883.json"}}],"schema_version":"1.8.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"}]}