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8.1
CVE-2026-66884: oidc_plug allows login without session or state, bypassing CSRF protection
CVE-2026-66884 · published 3 months ago
Summary
The oidc_plug component that handles authentication callbacks can accept requests that lack a proper login session or the required state value, causing the usual security checks to be skipped. As a result, an attacker could trick a user into completing a login flow they never started, giving the attacker access to the user's activity under the attacker's account. Update to a version that validates the session and state parameters, or add custom checks to reject such incomplete callback requests.
What to do
The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.
Affected software
| Vendor | Product | Affected versions |
|---|---|---|
| erlang ecosystem foundation | oidcc_plug |
< 0.5.0 < 97d75afc57826dca31989b47d6e2a3c136039917 |
Original advisory text
Oidcc.Plug.AuthorizationCallback accepts callbacks with no authorize session or no state parameter, defeating CSRF protection
Cross-Site Request Forgery vulnerability in Erlang Ecosystem Foundation oidcc_plug (Oidcc.Plug.AuthorizationCallback module) allows an attacker to make a victim's browser complete an authorization flow the victim never initiated.
This vulnerability is associated with program file lib/oidcc/plug/authorization_callback.ex and program routine Oidcc.Plug.AuthorizationCallback.call/2.
A callback request that carries no Oidcc.Plug.Authorize session is processed with every security check disabled rather than being rejected. call/2 substitutes permissive defaults for the absent session, and each downstream check treats its value as nothing to compare and returns :ok, so the nonce, state, PKCE, peer IP and user agent checks are all skipped. A separate clause of check_state/2 also accepts a state-less request when a verifier is present.
An attacker obtains an authorization code for their own provider account, then induces the victim to visit the callback endpoint with that code and no state parameter. The application signs the victim in as the attacker, so the victim's subsequent actions occur in the attacker's account where the attacker can read them. Applications reusing one callback for both signing in and linking a provider account are further exposed to account takeover, the attacker's account becoming linked to the victim's.
The permissive fallback serves no conforming flow. Third-party-initiated login reaches a relying party at a separate login initiation endpoint and causes it to send a fresh authentication request, and this library implements no such endpoint. Oidcc.Plug.Authorize always sends a state parameter, which an authorization server must echo, so no legitimate callback lacks one.
This issue affects oidcc_plug: from 0.2.0-beta.1 before 0.5.0.
This vulnerability is associated with program file lib/oidcc/plug/authorization_callback.ex and program routine Oidcc.Plug.AuthorizationCallback.call/2.
A callback request that carries no Oidcc.Plug.Authorize session is processed with every security check disabled rather than being rejected. call/2 substitutes permissive defaults for the absent session, and each downstream check treats its value as nothing to compare and returns :ok, so the nonce, state, PKCE, peer IP and user agent checks are all skipped. A separate clause of check_state/2 also accepts a state-less request when a verifier is present.
An attacker obtains an authorization code for their own provider account, then induces the victim to visit the callback endpoint with that code and no state parameter. The application signs the victim in as the attacker, so the victim's subsequent actions occur in the attacker's account where the attacker can read them. Applications reusing one callback for both signing in and linking a provider account are further exposed to account takeover, the attacker's account becoming linked to the victim's.
The permissive fallback serves no conforming flow. Third-party-initiated login reaches a relying party at a separate login initiation endpoint and causes it to send a fresh authentication request, and this library implements no such endpoint. Oidcc.Plug.Authorize always sends a state parameter, which an authorization server must echo, so no legitimate callback lacks one.
This issue affects oidcc_plug: from 0.2.0-beta.1 before 0.5.0.
References
- https://github.com URL
- https://repo.hex.pm URL
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66884... Vendor Advisory
- https://cna.erlef.org/cves/CVE-2026-66884.html URL
- https://osv.dev/vulnerability/EEF-CVE-2026-66884 URL
- https://github.com/erlef/oidcc_plug/security/advisories/GHSA-fg66-w5gp-22cr Vendor Advisory
- https://github.com/erlef/oidcc_plug/commit/97d75afc57826dca31989b47d6e2a3c136039... Patch
- https://nvd.nist.gov/vuln/detail/CVE-2026-66884 Vendor Advisory
- https://github.com/erlef/oidcc_plug Product
Internet-facing
60 days
Internal
At next upgrade
- Not known to be exploited
- Needs hands-on effort to exploit
- Gives an attacker partial control
Severity
8.1
High
Type
CWE-352Cross-Site Request Forgery (CSRF)
Timeline
Published4 Aug 2026
Updated4 Nov 2026
First seen4 Aug 2026
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