[NT] AdSubtract Proxy ACL Bypass Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 06/09/03

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Date: 9 Jun 2003 21:05:28 +0200

    The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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      AdSubtract Proxy ACL Bypass Vulnerability
    ------------------------------------------------------------------------

    SUMMARY

     <http://www.adsubtract.com/products.html> AdSubtract is "one of the
    leading products in the banner-ad blocking software market. It is
    frequently bundled with modems from several leading manufacturers and has
    an estimated installed user base in the millions".

    DETAILS

    Vulnerable systems:
     * AdSubtract / AdSubtract Pro version 2.55 and below

    AdSubtract is a proxy server designed to block pop-ups, banner ads,
    animations, sounds, and unwanted cookies. It typically runs as a service
    on the computer for which it is acting as a proxy, although it can be
    configured to act as a proxy server for an entire LAN. By default it
    listens for proxy connections on port 4444 and 11523 on all interfaces,
    but has access control so that only localhost (127.0.0.1) can use the
    service by default.

    Due to a design flaw, the access-control mechanism can be fooled into
    passing traffic for any source. An attacker can set up a PTR record for a
    host in the attacker's domain using a hostname such as
    "127.0.0.1.example.com". The AdSubtract server will do reverse DNS
    resolution on the IP address and will mistakenly authorize the connection
    based on finding the string "127.0.0.1" in the hostname.

    Logging of HTTP requests is turned off by default, so no record of any
    abuse will be found on the system being attacked.

    Vendor Status:
    Vendor was notified on May 5, 2003. Confirmation of the notification was
    received but no further response was given, despite several emails sent
    inquiring on the status of an updated version.

    Solution:
    At the time of this release, the vendor has not provided an updated
    version of the software to fix the vulnerability. Therefore, it is our
    recommendation to remove AdSubtract from any computer directly connected
    to the Internet.

    Sites who use proxy-testing software to deny connections from open proxies
    may want to include the conditions for this ACL bypass in their test
    parameters.

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:advisories@lurhq.com> LURHQ.

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