CVE-2026-81888 in hono
Summary
by MITRE • 08/31/2026
@hono/oauth-providers is Authentication middleware for Hono. Prior to version 0.8.6, the built-in social login providers accept an OAuth callback even when the `state` value is absent on both sides, so the anti-CSRF check passes for a callback that never came from a genuine login attempt. This defeats the `state`-based CSRF protection under default usage. Version 0.8.6 has a patch.
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Analysis
by VulDB Data Team • 08/31/2026
The vulnerability identified in hono/oauth-providers prior to version 0.8.6 represents a critical failure in implementing state-based Cross-Site Request Forgery (CSRF) protections for OAuth authentication flows. In standard OAuth implementations, the `state` parameter serves as a crucial security mechanism designed to ensure that an authorization response corresponds to a specific client-initiated request. This token is typically generated by the application and stored securely on the server side before redirecting the user to the identity provider. Upon redirection back from the provider, the application validates this state value against its internal records to confirm legitimacy. However, in versions of hono/oauth-providers preceding 0.8.6, the middleware logic was flawed such that it accepted OAuth callback requests even when the `state` parameter was entirely absent on both the request and the server-side storage. This oversight effectively nullifies the anti-CSRF protection mechanism under default usage configurations, allowing an attacker to forge authentication responses without needing to replicate or guess a valid state token.
From a technical perspective, this flaw aligns with CWE-352, which describes Cross-Site Request Forgery (CSRF). The absence of strict validation for the `state` parameter means that any arbitrary OAuth callback response can be processed by the application as if it were part of a legitimate login flow initiated by an authenticated user. An attacker could potentially exploit this by crafting malicious requests or manipulating redirect URIs to trigger authentication callbacks without proper authorization context. This undermines the integrity of the session establishment process, as the server cannot distinguish between a genuine callback resulting from a user's interaction and a forged response designed to hijack sessions or escalate privileges. The vulnerability is particularly dangerous because it operates silently under default settings, meaning many applications relying on this middleware would be exposed without explicit configuration errors by developers who assume standard security practices are enforced automatically.
The operational impact of this vulnerability extends beyond simple session hijacking. By bypassing the state validation, an attacker could potentially force a user to authenticate with a malicious OAuth provider or manipulate the authentication outcome in ways that compromise account integrity. In scenarios where automatic account linking is enabled based on social identity data, this flaw could allow attackers to associate victim accounts with attacker-controlled identities, leading to unauthorized access and potential data exfiltration. Furthermore, because the vulnerability affects the core middleware used for handling OAuth callbacks, it impacts all applications integrating @hono/oauth-providers without custom overrides or additional security layers. The lack of state validation creates a predictable attack vector that can be automated, increasing the risk of widespread compromise across systems utilizing this library.
To mitigate this vulnerability, organizations must upgrade to version 0.8.6 or later of @hono/oauth-providers, which includes the necessary patches to enforce strict `state` parameter validation. For applications unable to immediately update due to dependency constraints, implementing a custom middleware layer that explicitly checks for the presence and validity of the state token before processing OAuth callbacks is recommended as an interim measure. Developers should also ensure that their security configurations adhere to industry best practices by verifying that all required parameters are present and validated against server-side records during every step of the authentication flow. Regular audits of third-party dependencies and adherence to secure coding standards, such as those outlined in OWASP guidelines for session management and CSRF prevention, will help maintain robust protection against similar attacks in future updates.