CVE-2017-7674 in Tomcat
Summary
by MITRE
The CORS Filter in Apache Tomcat 9.0.0.M1 to 9.0.0.M21, 8.5.0 to 8.5.15, 8.0.0.RC1 to 8.0.44 and 7.0.41 to 7.0.78 did not add an HTTP Vary header indicating that the response varies depending on Origin. This permitted client and server side cache poisoning in some circumstances.
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Analysis
by VulDB Data Team • 12/15/2022
The vulnerability identified as CVE-2017-7674 represents a critical security flaw in Apache Tomcat's Cross-Origin Resource Sharing (CORS) implementation that affects multiple versions across different release lines. This issue stems from the improper handling of HTTP response headers within Tomcat's CORS filter mechanism, specifically the absence of the Vary header in responses that are influenced by the Origin request header. The omission creates a fundamental weakness in the application's security posture by failing to properly signal to caching mechanisms that responses should be treated differently based on the originating domain, thereby exposing applications to potential cache poisoning attacks that could be exploited by malicious actors.
The technical root cause of this vulnerability lies in the CORS filter's failure to implement proper HTTP header management according to established web security best practices. When a CORS request is processed, the server should include a Vary: Origin header in its response to indicate that the response content varies based on the Origin header value. Without this header, HTTP caches at various levels including proxies, CDNs, and browser caches may incorrectly store and serve responses intended for one origin to requests from another origin. This behavior creates a cache poisoning scenario where attackers can manipulate cached responses to deliver malicious content to unsuspecting users, effectively bypassing the CORS security controls that are meant to protect against cross-origin attacks.
From an operational impact perspective, this vulnerability creates significant risks for organizations relying on Apache Tomcat for web application deployment, particularly those handling sensitive data or implementing CORS-based access controls. The vulnerability can be exploited to deliver malicious content to users by manipulating cache servers to serve inappropriate responses, potentially leading to data breaches, session hijacking, or other forms of cross-site attacks. The attack surface is particularly concerning because it affects multiple versions of Tomcat across different major release lines, meaning that organizations with legacy systems or those using older versions may be vulnerable to exploitation without immediate awareness.
The security implications of this vulnerability align with CWE-1004, which addresses the weakness of insufficient HTTP header handling in web applications, and can be mapped to ATT&CK technique T1190, which involves exploiting vulnerabilities in web applications to conduct cache poisoning attacks. Organizations should implement immediate mitigations including updating to patched versions of Apache Tomcat, ensuring proper header configuration, and implementing additional security controls such as Content Security Policy headers to provide defense-in-depth. The vulnerability demonstrates the critical importance of proper HTTP header management in web security implementations and highlights how seemingly minor oversights in web application frameworks can create significant security risks that affect millions of users across various organizations.