CVE-2026-12740 in Plack::Middleware::OAuth
Summary
by MITRE • 07/04/2026
Plack::Middleware::OAuth versions through 0.10 for Perl do not support the OAuth 2.0 state parameter.
RequestTokenV2 builds the provider authorization redirect without issuing a state value, and AccessTokenV2 exchanges the callback code and registers the resulting token into the session (register_session) without verifying that the callback corresponds to an authorization request this session initiated.
Any application that uses this middleware for OAuth 2.0 login is exposed to login cross-site request forgery: because the callback is not bound to the session that began the flow, an attacker who starts an authorization with their own provider account can deliver the resulting callback to a victim, causing the victim's session to complete the attacker's authorization and associating the attacker's provider identity and access token with that session. Where the application persists this as an account link, the attacker may retain access to the victim's account through their own provider credentials.
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Analysis
by VulDB Data Team • 07/04/2026
This vulnerability in Plack::Middleware::OAuth versions through 0.10 represents a critical security flaw that directly impacts the integrity of OAuth 2.0 authentication flows within perl applications. The middleware fails to implement proper state parameter handling, which is a fundamental security mechanism designed to prevent cross-site request forgery attacks. The absence of state parameter validation creates a scenario where an attacker can manipulate the OAuth flow by initiating their own authorization request and then redirecting a victim's browser to their callback endpoint, effectively hijacking the victim's session and associating it with the attacker's provider credentials.
The technical implementation flaw stems from the RequestTokenV2 component which generates authorization redirects without including a state parameter, while AccessTokenV2 processes callbacks without validating that these requests originated from the same session that initiated the authorization flow. This design bypasses the core security principle that OAuth 2.0 state parameters should be generated per-session and validated upon callback to ensure that the authorization request and response are properly correlated. The vulnerability maps directly to CWE-352 Cross-Site Request Forgery, as it allows attackers to perform actions on behalf of users without their knowledge or consent.
The operational impact of this vulnerability is severe and can lead to complete account takeover scenarios within applications that rely on this middleware for OAuth 2.0 authentication. When an application persists the authenticated user's identity and access token into the session, an attacker who successfully manipulates the authorization flow can gain permanent access to the victim's account using their own provider credentials. This creates a persistent security risk where the attacker maintains access even after the initial attack window has passed. The vulnerability also aligns with ATT&CK technique T1566.002 for credential access through social engineering, as attackers can exploit this flaw to impersonate legitimate users.
Applications using this middleware for OAuth 2.0 login are particularly vulnerable because they lack the session binding mechanism that should prevent unauthorized callback processing. The attack scenario becomes possible due to the absence of proper validation that ensures callbacks are only accepted from sessions that initiated the authorization process, allowing attackers to deliver malicious callbacks that complete unauthorized authentication flows. Organizations should immediately upgrade to versions that properly implement OAuth 2.0 state parameter handling or implement additional mitigations such as custom session validation logic and callback URL verification mechanisms to prevent exploitation of this vulnerability.