EEF-CVE-2026-66883
- Source
- https://cna.erlef.org/osv/EEF-CVE-2026-66883.html
- Import Source
- https://cna.erlef.org/osv/EEF-CVE-2026-66883.json
- JSON Data
- https://api.osv.dev/v1/vulns/EEF-CVE-2026-66883
- Aliases
-
- CVE-2026-66883
- GHSA-w5r8-m75h-98fc
- Published
- 2026-08-04T11:46:05.191Z
- Modified
- 2026-08-04T12:11:01.318583837Z
- Severity
-
- 6.3 (Medium) CVSS_V4 - 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 CVSS Calculator
- Summary
- Oidcc.Plug.Authorize user agent session binding inert due to case-sensitive header lookup
- Details
-
Summary
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.
This 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.
Oidcc.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.
The 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.
This issue affects oidcc_plug: from 0.1.0-alpha.3 before 0.5.0.
- Database specific
{ "cpe_ids": [ "cpe:2.3:a:erlef:oidcc_plug:*:*:*:*:*:erlang:*:*" ], "cwe_ids": [ "CWE-178" ], "capec_ids": [ "CAPEC-60" ] }- References
- Credits
-
-
- Mathias Polligkeit - FINDER
-
- Jonatan Männchen / EEF - REMEDIATION_DEVELOPER
-
- Mathias Polligkeit - REMEDIATION_REVIEWER
-
- Jonatan Männchen / EEF - COORDINATOR
-
Affected packages
Hex / oidcc_plug
Package
- Name
- oidcc_plug
- Purl
- pkg:hex/oidcc_plug