Directory Traversal

Affecting org.apache.tomcat:tomcat-catalina artifact, versions [9.0.0M1,9.0.5) || [8.5.0,8.5.28) || [8.0.0RC1,8.0.50) || [7.0.0,7.0.85)

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Overview

org.apache.tomcat:tomcat-catalina is a Tomcat Servlet Engine Core Classes and Standard implementations.

Affected versions of this package are vulnerable to Directory Traversal. Security constraints defined by annotations of Servlets were only applied once a Servlet had been loaded. Because security constraints defined in this way apply to the URL pattern and any URLs below that point, it was possible - depending on the order Servlets were loaded - for some security constraints not to be applied. This could have exposed resources to users who were not authorised to access them.

Details

A Directory Traversal attack (also known as path traversal) aims to access files and directories that are stored outside the intended folder. By manipulating files with "dot-dot-slash (../)" sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration, and other critical system files.

Directory Traversal vulnerabilities can be generally divided into two types:

  • Information Disclosure: Allows the attacker to gain information about the folder structure or read the contents of sensitive files on the system.

st is a module for serving static files on web pages, and contains a vulnerability of this type. In our example, we will serve files from the public route.

If an attacker requests the following URL from our server, it will in turn leak the sensitive private key of the root user.

curl http://localhost:8080/public/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/root/.ssh/id_rsa

Note %2e is the URL encoded version of . (dot).

  • Writing arbitrary files: Allows the attacker to create or replace existing files. This type of vulnerability is also known as Zip-Slip.

One way to achieve this is by using a malicious zip archive that holds path traversal filenames. When each filename in the zip archive gets concatenated to the target extraction folder, without validation, the final path ends up outside of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.

The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicious file will result in traversing out of the target folder, ending up in /root/.ssh/ overwriting the authorized_keys file:

2018-04-15 22:04:29 .....           19           19  good.txt
2018-04-15 22:04:42 .....           20           20  ../../../../../../root/.ssh/authorized_keys

Remediation

Upgrade org.apache.tomcat:tomcat-catalina to version 9.0.5, 8.5.28, 8.0.50, 7.0.85 or higher.

References

CVSS Score

6.5
medium severity
  • Attack Vector
    Network
  • Attack Complexity
    Low
  • Privileges Required
    Low
  • User Interaction
    None
  • Scope
    Unchanged
  • Confidentiality
    High
  • Integrity
    None
  • Availability
    None
CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Credit
Unknown
CVE
CVE-2018-1305
CWE
CWE-22
Snyk ID
SNYK-JAVA-ORGAPACHETOMCAT-32110
Disclosed
23 Feb, 2018
Published
25 Feb, 2018