[VulnWatch] iDEFENSE Security Advisory 01.18.05 - Multiple Unix/Linux Vendor Xpdf makeFileKey2 Stack Overflow

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Date: 01/18/05

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    Multiple Unix/Linux Vendor Xpdf makeFileKey2 Stack Overflow

    iDEFENSE Security Advisory 01.18.05
    www.idefense.com/application/poi/display?id=186&type=vulnerabilities
    January 18, 2005

    I. BACKGROUND

    Xpdf is an open-source viewer for PDF files. More information is
    available at the following site:

    http://www.foolabs.com/xpdf/

    II. DESCRIPTION

    Remote exploitation of a buffer overflow vulnerability in the xpdf PDF
    viewer included in multiple Unix and Linux distributions could allow for

    arbitrary code execution as the user viewing a PDF file.

    The vulnerability specifically exists due to insufficient bounds
    checking while processing a PDF file that provides malicious values in
    the /Encrypt /Length tag. The offending code can be found in the
    Decrypt::makeFileKey2 function in the source file xpdf/Decrypt.cc.

    GBool Decrypt::makeFileKey2(int encVersion, int encRevision,
                                int keyLength, GString *ownerKey,
                                GString *userKey, int permissions,
                                GString *fileID, String *userPassword,
                                Guchar *fileKey) {
          Guchar *buf;
          Guchar test[32];
          Guchar fState[256];
          Guchar tmpKey[16];
          Guchar fx, fy;
          int len, i, j;
          GBool ok;
          ...

                memcpy(test, userKey->getCString(), 32);
                for (i = 19; i >= 0; --i) {
                      for (j = 0; j < keyLength; ++j) {
    [overflow] tmpKey[j] = fileKey[j] ^ i;
                      }
                ...
          }
          ...
    }

    In this piece of code, the keyLength value is ultimately supplied by the

    PDF file. This allows an attacker to specify an arbitrarily large value
    and overwrite portions of stack memory. As a consequence, arbitrary code

    execution is possible.

    III. ANALYSIS

    Successful exploitation of this vulnerability leads to arbitrary code
    execution as the user who opened the malicious file. An attacker would
    have to convince a target to open the provided file in order to exploit
    this vulnerability, thus lessening the impact.

    Exploitation can be performed reliably, especially with knowledge of the

    target system.

    IV. DETECTION

    iDEFENSE has confirmed the existence of this vulnerability in version
    3.00 of xpdf. It is suspected previous versions are vulnerable.

    The following Linux vendors may be affected by this vulnerability:

            Novell Inc. (SUSE)
            Red Hat Inc.
            The Fedora Project
            Debian Project
            Gentoo Foundation Inc.
            The FreeBSD Project
            OpenBSD

    V. WORKAROUND

    Only open PDF files from trusted individuals.

    VI. VENDOR RESPONSE

    A patch to address this issue is available at:

        ftp://ftp.foolabs.com/pub/xpdf/xpdf-3.00pl3.patch

    Updated binaries (ver. 3.00pl3) to address this issue are available at:

        http://www.foolabs.com/xpdf/download.html

    VII. CVE INFORMATION

    The Common Vulnerabilities and Exposures (CVE) project has assigned the
    names CAN-2005-0064 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

    01/06/2005 Initial vendor notification
    01/12/2005 Initial vendor response
    01/18/2005 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

    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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