Proof of concept
Do your applications use this vulnerable package?
1 Jul 2021
1 Jul 2021
How to fix?
webrick to version 1.4.0.beta1 or higher.
webrick is a HTTP server toolkit that can be configured as an HTTPS server, a proxy server, and a virtual-host server.
Affected versions of this package are vulnerable to Directory Traversal. WEBrick, when using NTFS or FAT filesystems, allows remote attackers to read arbitrary CGI files via any of the following trailing characters in the URI:
%2e(encoded dot), or
This is possibly related to the
WEBrick::HTTPServer.new functionality, and the
Accessing the following URIs to gain access to file.cgi: http://SERVER/file.cgi. http://SERVER/file.cgi%2e
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
If an attacker requests the following URL from our server, it will in turn leak the sensitive private key of the root user.
%2e is the URL encoded version of
- Writing arbitrary files: Allows the attacker to create or replace existing files. This type of vulnerability is also known as
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
2018-04-15 22:04:29 ..... 19 19 good.txt 2018-04-15 22:04:42 ..... 20 20 ../../../../../../root/.ssh/authorized_keys