CVE-2024-38819 is a critical security vulnerability that affects WebMvc.fn and WebFlux.fn functional web frameworks in Spring based applications serving static resources. Due to insufficient validation of the input paths in these frameworks, the applications are exposed to path traversal attacks. This potentially allows an attacker to craft malicious HTTP requests in order to gain access to files on the system, which the targeted Spring application has access to.

Exploit Details

A path traversal attack or directory traversal attack is a type of security vulnerability where an attacker manipulates user input (usually a file or directory path) to gain unauthorized access to files and directories outside the intended scope. In the context of CVE-2024-38819, an attacker can craft malicious HTTP requests formed with the appropriate "../" sequences to access files they are not supposed to. This ultimately relies on insufficient input validation within the WebMvc.fn or WebFlux.fn frameworks.

For example, consider a Spring application with the following code snippet where it maps a GET request to serve static files using WebMvc.fn:

RouterFunction<ServerResponse> route = route()
  .GET("/static/**", req -> {
    String file = req.pathVariable("file");
    return ServerResponse.ok().body(fromPath(Paths.get(STATIC_RESOURCES_PATH, file)));
  })
  .build();

An attacker might exploit the vulnerability by making the following HTTP requests

GET /static/../../../../etc/passwd
GET /static/../../../../../var/log/messages

If successful, these requests would lead to unauthorized access to the specified files.

Mitigation

The mitigation for CVE-2024-38819 must be applied at the application level. Developers should properly validate and sanitize user input before handling files and directory paths. One may follow the guidelines in the Spring framework official documentation and use the Spring-provided utility methods ensuring that the file operations stay within the intended directory structure.

The following code snippet shows an example of how to sanitize user input in a WebMvc.fn or WebFlux.fn application:

RouterFunction<ServerResponse> route = route()
  .GET("/static/**", req -> {
    String file = req.pathVariable("file");

    // Sanitize the user input (file variable)
    String sanitizedPath = UriUtils.extractFileExtension(file);
    sanitizedPath = sanitizedPath.replace("..", "");
    sanitizedPath = sanitizedPath.replace("%", "");

    return ServerResponse.ok().body(fromPath(Paths.get(STATIC_RESOURCES_PATH, sanitizedPath)));
  })
  .build();

Applying proper input validation and sanitization techniques can mitigate the CVE-2024-38819 vulnerability and prevent attackers from exploiting path traversal attacks.

The Common Vulnerabilities and Exposures (CVE) database entry for CVE-2024-38819

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-38819

The official Spring Framework documentation

https://docs.spring.io/spring-framework/docs/current/reference/html/web-reactive.html#webflux-fn

A detailed explanation of path traversal attacks by OWASP

https://owasp.org/www-community/attacks/Path_Traversal

Conclusion

CVE-2024-38819 is a critical security vulnerability affecting the WebMvc.fn and WebFlux.fn functional web frameworks in Spring applications serving static resources. It is essential for developers to pay attention to validating and sanitizing user input to file and directory paths to avoid potential path traversal attacks. By following the guidelines in the Spring framework documentation and applying proper input validation and sanitization techniques, developers can ensure robust security and protect their applications from unauthorized file access.

Timeline

Published on: 12/19/2024 18:15:10 UTC