CVE-2026-47889 in Spring Framework
Summary
by MITRE • 08/27/2026
A WebFlux application running on the Jetty 12 Core reactive adapter serializes response cookies without the sameSite attribute. Spring Framework 7.0.0 - 7.0.8 Spring Framework 6.2.0 - 6.2.19
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Analysis
by VulDB Data Team • 08/27/2026
The vulnerability identified in this advisory stems from a configuration oversight within the reactive web server adapter for Jetty Core version 12, specifically when utilized with Spring Framework versions ranging from 7.0.0 to 7.0.8 and 6.2.0 to 6.2.19. In modern web application development, particularly those leveraging reactive programming models via WebFlux, the handling of HTTP cookies is critical for maintaining session integrity and user state across requests. The core technical flaw lies in the serialization process where response cookies are emitted without explicitly setting the SameSite attribute. This omission occurs because the underlying Jetty 12 Core adapter does not automatically infer or apply a default SameSite policy when constructing cookie headers, leaving the browser to rely on its own legacy defaults which historically defaulted to no restriction unless specified otherwise by the application developer.
From a security architecture perspective, this flaw directly maps to CWE-697, Incorrect Comparison, and more accurately CWE-1004, Sensitive Cookie Without 'SameSite' Attribute, as it involves the failure to enforce expected security properties on sensitive data transmission mechanisms. The absence of the SameSite attribute means that cookies are sent with all cross-site requests initiated by the victim user's browser. This behavior creates a significant attack surface for Cross-Site Request Forgery attacks where an attacker can craft malicious links or forms that trigger state-changing actions in the vulnerable application while the user is authenticated, as the browser will automatically attach the session cookie to these unauthorized requests. Furthermore, it exacerbates risks associated with CSRF token theft if tokens are stored within cookies rather than headers, although modern best practices often mitigate this by storing tokens in memory or HttpOnly flags combined with SameSite Strict settings.
The operational impact of this vulnerability is severe for applications handling sensitive user data or performing administrative actions without additional protective layers. Attackers can exploit the lack of same-site restrictions to perform unauthorized state changes such as fund transfers, password resets, or account modifications by tricking authenticated users into visiting malicious sites that submit requests to the vulnerable application. The reactive nature of WebFlux does not inherently protect against this class of attack; rather, it requires explicit configuration at the framework level to ensure security headers and cookie attributes are correctly propagated through the non-blocking I/O pipeline. Without proper mitigation, organizations face potential data breaches, unauthorized access, and compliance violations related to inadequate session management controls under standards like OWASP Top 10 which consistently list Broken Access Control and Cross-Site Request Forgery as critical risks.
To mitigate this vulnerability, developers must explicitly configure the SameSite attribute for all cookies within their Spring WebFlux applications. This can be achieved by implementing a custom ServerCookieDecoder or configuring cookie settings at the application level to enforce values such as Lax or Strict depending on the specific security requirements of each endpoint. For instance, setting SameSite=Strict provides the highest level of protection against CSRF but may impact user experience for legitimate cross-site navigation, while SameSite=Lax offers a balanced approach by allowing cookies with top-level navigations. Additionally, ensuring that sensitive cookies are marked as HttpOnly and Secure further reduces the risk of cookie theft via XSS attacks which often accompany CSRF exploits in real-world scenarios. Upgrading to patched versions of Spring Framework where this behavior is corrected or applying these explicit configuration overrides will effectively neutralize the threat vector associated with unvalidated same-site policies.