CVE-2026-49455 in Waku
Summary
by MITRE • 09/03/2026
Waku is the minimal React framework. Prior to version 1.0.0-beta.1, Waku's RSC request dispatcher invokes server actions without validating the request's Origin (or Sec-Fetch-Site) header. A cross-origin web attacker can therefore cause a victim browser to issue an authenticated POST to a registered server action endpoint using a CORS-safelisted content type (text/plain), which does not trigger a preflight. Any state-mutating server action that the application exposes via 'use server' can be invoked with the victim's cookies attached. This issue has been patched in version 1.0.0-beta.1.
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Analysis
by VulDB Data Team • 09/03/2026
The vulnerability identified in Waku, specifically within versions prior to 1.0.0-beta.1, represents a critical failure in cross-origin request validation for React Server Components (RSC) server actions. As the minimal React framework designed to streamline server-side rendering and state management, Waku relies on specific HTTP headers to enforce security boundaries between different origins. The core technical flaw lies in the RSC request dispatcher's handling of POST requests intended to invoke registered server actions. Specifically, the implementation fails to validate the Origin header or the Sec-Fetch-Site header before processing these requests. This omission creates a significant gap in the application's defense-in-depth strategy, allowing malicious actors to bypass standard browser security mechanisms that are typically designed to prevent unauthorized cross-origin interactions.
From an operational perspective, this flaw enables Cross-Site Request Forgery (CSRF) attacks against authenticated users of applications built with Waku. An attacker can craft a malicious webpage or script that forces a victim's browser to send a POST request to the vulnerable server action endpoint. Because the vulnerability exploits CORS-safelisted content types such as text/plain, the attack does not trigger a preflight OPTIONS request. Preflight requests are a standard part of the Cross-Origin Resource Sharing protocol used by browsers to check if a cross-origin request is safe; their absence in this scenario allows the malicious POST request to proceed directly without prior authorization checks from the server. Consequently, any state-mutating server action exposed via the use server directive can be executed with the victim's session cookies attached, effectively allowing the attacker to perform actions on behalf of the authenticated user.
This vulnerability aligns closely with CWE-352, which describes Cross-Site Request Forgery (CSRF), as it involves tricking a user into performing an unwanted action while authenticated. Furthermore, from the perspective of the MITRE ATT&CK framework, this exploit technique falls under T1089, Disabling Security Tools or Mechanisms, specifically by bypassing browser-enforced security policies like CORS preflight checks to achieve unauthorized state changes. The impact is severe because it compromises the integrity and confidentiality of user data, potentially leading to account takeover, unauthorized transactions, or modification of critical application states depending on the specific server actions exposed.
The issue has been addressed in version 1.0.0-beta.1 through the implementation of strict origin validation for incoming requests targeting server action endpoints. To mitigate similar risks in other frameworks or custom implementations, developers should ensure that all state-mutating cross-origin POST requests are validated against a whitelist of allowed origins using both the Origin and Sec-Fetch-Site headers. Additionally, implementing anti-CSRF tokens remains a robust defense-in-depth measure. Applications relying on React Server Components must verify that incoming requests originate from trusted sources before executing any logic that modifies server-side state or database records. Regular security audits focusing on API endpoint authentication and authorization flows are recommended to prevent the exposure of sensitive actions to untrusted origins.