Directory Traversal

Affecting fury-adapter-swagger package, versions <0.9.7 >=0.2.0 || ~0.8.0-pre

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Overview

fury-adapter-swagger is Swagger 2.0 parser for Fury.js. Fury is an SDK that helps loading and HTTP API description format (like swagger) and creates a uniformed format which is easy to work with. The swagger description document is a JSON or YAML file and per specification allows inclusion of other documents by reference. Fury takes this JSON file and outputs it as a JS object. This may allow any user and in particular a malicious user to edit the swagger document in an online editor and write and file into it's references, and in particular any file on the applications hosting server (e.g. /etc/passwrd). The document will try to include the contents of the referenced file during parsing and may expose confidential information like passwords, environment variables, DB Connection credentials, etc. Also, a possible Denial of service may occur due to /dev/zero consuming all available memory.

Thanks to Adam Kliment and Honza Javorek for finding and reporting this vulnerability to us.

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 fury-adapter-swagger to version 0.9.7 or higher.

References

CVSS Score

7.3
high severity
  • Attack Vector
    Network
  • Attack Complexity
    Low
  • Privileges Required
    None
  • User Interaction
    None
  • Scope
    Unchanged
  • Confidentiality
    Low
  • Integrity
    Low
  • Availability
    Low
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Credit
Adam Kliment
CVE
CVE-2016-1000249
CWE
CWE-22
Snyk ID
npm:fury-adapter-swagger:20161024
Disclosed
23 Oct, 2016
Published
11 Jan, 2017