uWSGI < 2.0.17 - Directory Traversal

# Exploit Title: uWSGI PHP Plugin Directory Traversal
# Date: 01-03-2018
# Exploit Author: Marios Nicolaides - RUNESEC
# Reviewers: Simon Loizides and Nicolas Markitanis - RUNESEC
# Vendor Homepage: https://uwsgi-docs.readthedocs.io
# Affected Software: uWSGI PHP Plugin before 2.0.17
# Tested on: uWSGI 2.0.12 and 2.0.15
# CVE: CVE-2018-7490
# Category: Web Application


OVERVIEW
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The uWSGI PHP plugin before 2.0.17 is vulnerable to Directory Traversal when used without specifying the "php-allowed-docroot" option.

The vulnerability exists due to improper validation of the file path when requesting a resource under the DOCUMENT_ROOT directory which is specified via "php-docroot".

A remote attacker could exploit this weakness to read arbitrary files from the vulnerable system using path traversal sequences ("..%2f").

This was tested on uWSGI 2.0.12 and 2.0.15. All versions before 2.0.17 are affected.


DETAILS
-------
The documentation of uWSGI states that the php-docroot option is used to jail our php environment to a project directory (http://uwsgi-docs.readthedocs.io/en/latest/PHP.html#run-php-apps-without-a-frontend-server).

	; jail our php environment to project_dir
	php-docroot = %(project_dir)

During testing it was observed that uWSGI was affected by a Directory Traversal vulnerability when executed as a standalone (without a front-end web server) along with the "php-docroot" option to enforce the DOCUMENT_ROOT of the web application.

    uwsgi --http-socket :1337 --protocol=http --plugin php --php-index index.php --php-docroot /home/testing/webapp/

An attacker could exploit this vulnerability by using path traversal sequences ("..%2f") to access sensitive information as demonstrated below:

    http://example.runesec.com:1337/..%2f..%2f..%2f..%2f..%2f..%2f..%2fetc/passwd

We noticed that when a Directory Traversal attack was performed, uWSGI was issuing the following security error:

    [uwsgi-fileserve] security error: /etc/passwd is not under /home/testing/webapp or a safe path

However, the contents of the requested file (i.e., /etc/passwd) were still returned to the user.

After searching the web for possible solutions, we noticed that the "php-allowed-docroot" option was previously added to uWSGI for better security and could be used to list the allowed document roots but no further details were available (http://lists.unbit.it/pipermail/uwsgi/2011-December/003180.html).

Upon further testing, we observed that when the "php-allowed-docroot" was used instead of the "php-docroot" option, it was not affected by Directory Traversal attacks.

    uwsgi --http-socket :1337 --protocol=http --plugin php --php-index index.php --php-allowed-docroot /home/testing/webapp/

After a very constructive and helpful talk with the uWSGI Project, they released an update which enforces a DOCUMENT_ROOT check when using the "php-docroot" option to prevent Directory Traversal attacks. Please see the MITIGATION section for more information.


IMPACT
------
An attacker could exploit this vulnerability to gain unauthorized read access to sensitive files located outside of the web root directory.


MITIGATION
----------
It is recommended to update to uWSGI 2.0.17 - https://uwsgi-docs.readthedocs.io/en/latest/Changelog-2.0.17.html


REFERENCES
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https://blog.runesec.com/2018/03/01/uwsgi-path-traversal/
https://uwsgi-docs.readthedocs.io/en/latest/Changelog-2.0.17.html
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-7490
https://nvd.nist.gov/vuln/detail/CVE-2018-7490
https://www.owasp.org/index.php/Testing_Directory_traversal/file_include_(OTG-AUTHZ-001)


TIMELINE
--------
26 June 2017 - uWSGI Project informed about the issue
26 February 2018 - uWSGI Project released a patch
1 March 2018 - Exploit publicly disclosed