(PT-2012-06) Positive Technologies Security Advisory
Security restrictions bypass in nginx for Windows

Vulnerable software

nginx for Windows
Version: 1.2.0 and earlier, 1.3.0 and earlier

Application link:
http://nginx.org/

Severity level

Severity level: Medium
Impact: Security restrictions bypass
Access Vector: Network exploitable 

CVSS v2:
Base Score: 5.0
Vector: (AV:N/AC:L/Au:N/C:P/I:N/A:N)

CVE: CVE-2011-4963

Software description

nginx [engine x] is a HTTP server, reversed proxy server, and also mail proxy server.

Vulnerability description

The specialists of the Positive Research center have a vulnerability detected "Security restrictions bypass" in nginx for Windows.

The system does not consider that NTFS allows users to address folders with extended syntax attribute, while matching the requested resource URL with locations defined in web server configuration. This allows attackers to bypass access restrictions set for static resources.

Exploitation

location ~/directory/ {
    deny all;
}

An attacker can bypass this restriction if he/she calls the resource as follows:

"/directory:$i30:$INDEX_ALLOCATION/file"
"/directory::$index_allocation/file"
"/directory./file"

How to fix

Update your software up to the latest version

For older versions the following configuration can be used as a workaround:

location ~ "(\.|:\$)" {
    deny all;
}

Advisory status

15.05.2012 - Vendor is notified
15.05.2012 - Vendor gets vulnerability details
05.06.2012 - Vendor releases fixed version and details
07.06.2012 - Public disclosure

Credits

The vulnerability was discovered by Vladimir Kochetkov, Positive Research Center (Positive Technologies Company)

References

http://en.securitylab.ru/lab/PT-2012-06
http://mailman.nginx.org/pipermail/nginx-announce/2012/000086.html

Reports on the vulnerabilities previously discovered by Positive Research:

http://ptsecurity.com/research/advisory/
http://en.securitylab.ru/lab/

About Positive Technologies

Positive Technologies www.ptsecurity.com is among the key players in the IT security market in Russia.

The principal activities of the company include the development of integrated tools for information security monitoring (MaxPatrol); providing IT security consulting services and technical support; development of the Securitylab leading Russian information security portal.

Among the clients of Positive Technologies, there are more than 40 state enterprises, more than 50 banks and financial organizations, 20 telecommunication companies, more than 40 plant facilities, as well as IT, service and retail companies from Russia, the CIS countries, the Baltic States, China, Ecuador, Germany, Great Britain, Holland, Iran, Israel, Japan, Mexico, the Republic of South Africa, Thailand, Turkey, and the USA.

Positive Technologies is a team of highly skilled developers, advisers and experts with years of vast hands-on experience. The company specialists possess professional titles and certificates; they are the members of various international societies and are actively involved in the IT security field development.