Erlang Ecosystem Foundation oidcc_plug up to 0.4.x Authorize module authorization_callback.ex authentication replay

Summaryinfo

A vulnerability was found in Erlang Ecosystem Foundation oidcc_plug up to 0.4.x. It has been classified as critical. Affected by this vulnerability is the function Oidcc.Plug.Authorize.call/Oidcc.Plug.AuthorizationCallback.call of the file lib/oidcc/plug/authorize.ex/lib/oidcc/plug/authorization_callback.ex of the component Authorize module. Performing a manipulation results in authentication replay. This vulnerability was named CVE-2026-66883. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability classified as critical has been found in Erlang Ecosystem Foundation oidcc_plug up to 0.4.x. This affects the function Oidcc.Plug.Authorize.call/Oidcc.Plug.AuthorizationCallback.call of the file lib/oidcc/plug/authorize.ex/lib/oidcc/plug/authorization_callback.ex of the component Authorize module. The manipulation with an unknown input leads to a authentication replay vulnerability. CWE is classifying the issue as CWE-294. A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes). This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-66883 since 07/28/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1040 according to MITRE ATT&CK.

Upgrading to version 0.5.0 eliminates this vulnerability.

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Productinfo

Vendor

• Erlang Ecosystem Foundation

Name

• oidcc_plug

Version

• 0.1
• 0.2
• 0.3
• 0.4

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