{"id":"CVE-2026-66883","published":"2026-08-04T12:16:36.163","lastModified":"2026-08-04T14:52:54.493","description":"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.","cvssScore":null,"cvssSeverity":null,"cvssVector":null,"cwes":["CWE-178"],"vendors":[],"products":[],"references":[{"url":"https://cna.erlef.org/cves/CVE-2026-66883.html","tags":[]},{"url":"https://github.com/erlef/oidcc_plug/commit/f15e52c5750aaba701104b10ed96cfac063bd557","tags":[]},{"url":"https://github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc","tags":[]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-66883","tags":[]},{"url":"https://github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc","tags":[]}],"exploitRefs":[{"url":"https://github.com/erlef/oidcc_plug/commit/f15e52c5750aaba701104b10ed96cfac063bd557","tags":[]},{"url":"https://github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc","tags":[]},{"url":"https://github.com/erlef/oidcc_plug/security/advisories/GHSA-w5r8-m75h-98fc","tags":[]}],"hasPoc":true,"ai":null}