Directory Traversal

Affecting scott-blanch-weather-app package, ALL versions

high severity

Overview

scott-blanch-weather-app is no longer supported and has been deprecated.

Affected versions of the package are vulnerable to Directory Traversal, which may allow access to sensitive files and data on the server. For example, requesting the following url /..%2f..%2fetc/passwd would result in /etc/passwd leak.

Thanks to Liang Gong for disclosing this vulnerability!

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 variables that reference 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 can be achieved using a specially crafted zip archive, that holds path traversal filenames. So when the filename gets concatenated to the target extraction folder, 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 malicous 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

There is no fix version for scott-blanch-weather-app.

References

Do your applications use this vulnerable package?

Credit
Liang Gong
CVE
CVE-2017-16184
CWE
CWE-22
Snyk ID
npm:scott-blanch-weather-app:20170505
Disclosed
05 May, 2017
Published
12 Jun, 2017