iDEFENSE Security Advisory 02.28.05: KPPP Privileged File Descriptor Leak Vulnerability

From: iDEFENSE Labs (labs-no-reply_at_idefense.com)
Date: 02/28/05

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To: <bugtraq@securityfocus.com>, <vulnwatch@vulnwatch.org>

    KPPP Privileged File Descriptor Leak Vulnerability

    iDEFENSE Security Advisory 02.28.05
    www.idefense.com/application/poi/display?id=208&type=vulnerabilities
    February 28, 2005

    I. BACKGROUND

    KPPP is a dialer and front end for pppd. It allows for interactive
    script generation and network setup. More information is available at:

        http://docs.kde.org/en/3.3/kdenetwork/kppp/

    II. DESCRIPTION

    Local exploitation of a privileged file descriptor leak in KPPP can
    allow attackers to hijack a system's domain name resolution function.

    The vulnerability specifically exists due to kppp's failure to properly
    close privileged file descriptors. Typically, KPPP is installed setuid
    root and uses privilege separation to allow only certain functions of
    the PPP dialer to execute with elevated privileges. Communication
    between the privileged portion and non-privileged portion of kppp is
    done over a domain socket which does not properly get closed.

    A fix for a similar vulnerability was introduced to the kppp code base
    in 1998 as can be seen below:

        // close file descriptors
        for (int fd = 3; fd < 20; fd++)
          close(fd);

    This fix may be easily bypassed if an attacker opens 17 file descriptors
    before executing kppp. The loop will execute, closing the previously
    opened file descriptors and leave the remaining privileged file
    descriptor used to talk to the privileged component of kppp open for
    attackers. KPPP may be abused to gain read and write access to
    /etc/hosts and /etc/resolv.conf, thus giving attackers complete control
    over a system's domain resolution capabilities.

    III. ANALYSIS

    Exploitation allows local attackers to gain control over a system's
    domain name resolution function. Exploitation is trivial and allows an
    attacker to write to the two files typically providing the configuration
    for domain name resolution. Modifications of /etc/resolv.conf will allow
    the attacker to specify a malicious domain server which may return
    arbitrary responses to domain name lookups. Modifications to /etc/hosts
    will cause hostname resolution redirection without the need for an
    external domain server. This class of attack can be used to aid in
    phishing and social engineering attempts.

    IV. DETECTION

    iDEFENSE has confirmed the existence of this vulnerability in KPPP
    2.1.2. The vendor has confirmed that KPPP as included in KDE 3.1.5 and
    prior are affected. KDE 3.2.x and newer are not affected.

    Note that some Linux distributions which come with KPPP, such as Red
    Hat Linux, use a wrapper for executing X11 applications that require
    root privileges. This wrapper safely closes all file descriptors in the

    executed application.

    V. WORKAROUND

    As a workaround, temporarily remove the setuid bit from KPPP and
    manually gain root privileges before executing KPPP:

    chmod -s /usr/sbin/kppp

    VI. VENDOR RESPONSE

    A vendor advisory for this issue is available at:

       http://www.kde.org/info/security/advisory-20050228-1.txt

    A patch for KDE 3.1 is available from

       ftp://ftp.kde.org/pub/kde/security_patches :

       0e999df54963edd5f565b6d541f408d9 post-3.1.5-kdenetwork.diff

    VII. CVE INFORMATION

    The Common Vulnerabilities and Exposures (CVE) project has assigned the
    names CAN-2005-0205 to these issues. This is a candidate for inclusion
    in the CVE list (http://cve.mitre.org), which standardizes names for
    security problems.

    VIII. DISCLOSURE TIMELINE

    02/09/2005 Initial vendor notification
    02/09/2005 Initial vendor response
    02/28/2005 Coordinated public disclosure

    IX. CREDIT

    The discoverer of this vulnerability wishes to remain anonymous.

    Get paid for vulnerability research
    http://www.idefense.com/poi/teams/vcp.jsp

    Free tools, research and upcoming events
    http://labs.idefense.com

    X. LEGAL NOTICES

    Copyright (c) 2005 iDEFENSE, Inc.

    Permission is granted for the redistribution of this alert
    electronically. It may not be edited in any way without the express
    written consent of iDEFENSE. If you wish to reprint the whole or any
    part of this alert in any other medium other than electronically, please
    email customerservice@idefense.com for permission.

    Disclaimer: The information in the advisory is believed to be accurate
    at the time of publishing based on currently available information. Use
    of the information constitutes acceptance for use in an AS IS condition.
    There are no warranties with regard to this information. Neither the
    author nor the publisher accepts any liability for any direct, indirect,
    or consequential loss or damage arising from use of, or reliance on,
    this information.

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