CVE-2026-66884 Cross-site request forgery in oidcc plug
Attackers can bypass CSRF protections in oidcc_plug to sign victims into attacker-controlled accounts, leading to account takeover and data exposure.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-66884?
CVE-2026-66884 is a low-severity vulnerability in Erlang Ecosystem Foundation oidcc_plug, published on 4 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-352
Which versions are affected by CVE-2026-66884?
1 open source package ship an affected version, including oidcc_plug.
| Package | Affected | Fixed in |
|---|---|---|
oidcc_plug Hex | From 0.2.0-beta.1 | 0.5.0 |
How do I fix CVE-2026-66884?
Upgrade oidcc_plug to 0.5.0 or later.
Is CVE-2026-66884 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-66884 exists.
Sources
Also known as EEF-CVE-2026-66884, GHSA-fg66-w5gp-22cr.