[UNIX] Multiple UNIX/Linux Vendor Xpdf makeFileKey2 Stack Overflow

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To: list@securiteam.com
Date: 23 Jan 2005 14:38:37 +0200

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  Multiple UNIX/Linux Vendor Xpdf makeFileKey2 Stack Overflow
------------------------------------------------------------------------

SUMMARY

 <http://www.foolabs.com/xpdf/> Xpdf is an open-source viewer for PDF
files.

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.

DETAILS

Vulnerable Systems:
 * Xpdf Version 3.00 and prior

Immune Systems:
 * Xpdf Version 3.00pl3 or newer

The vulnerability specifically exists due to insufficient bounds checking
while processing a PDF file that provides malicious values in the /Encrypt
/Length tag.

Vulnerable Code:
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.

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.

Vendor Status:
A patch to address this issue is available at:
<ftp://ftp.foolabs.com/pub/xpdf/xpdf-3.00pl3.patch>
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>
http://www.foolabs.com/xpdf/download.html

Disclosure Timeline:
01/06/2005 - Initial vendor notification
01/12/2005 - Initial vendor response
01/18/2005 - Coordinated public disclosure

CVE Information:
 <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0064>
CAN-2005-0064

ADDITIONAL INFORMATION

The information has been provided by
<mailto:idlabs-advisories@idefense.com> iDEFENSE.
The original article can be found at:
<www.idefense.com/application/poi/display?id=186&type=vulnerabilities>
www.idefense.com/application/poi/display?id=186&type=vulnerabilities

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