[NEWS] IBM DB2 Buffer Overflow Vulnerabilities (rec2xml, generate_distfile)

From: SecuriTeam (support_at_securiteam.com)
Date: 12/27/04

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Date: 27 Dec 2004 10:40:29 +0200

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      IBM DB2 Buffer Overflow Vulnerabilities (rec2xml, generate_distfile)
    ------------------------------------------------------------------------

    SUMMARY

    IBM's DB2 database server contains a procedure, generate_distfile. This
    procedure suffers from a stack based buffer overflow vulnerability. IBM's
    DB2 database server contains a function, rec2xml, used to format a string
    in XML. This function suffers from a stack based buffer overflow
    vulnerability.

    DETAILS

    Vulnerable Systems:
     * DB2 8.1/7.x

    Buffer Overflow Vulnerability in rec2xml:
    By passing an overly long 3rd parameter to the rec2xml function a stack
    based buffer can be overflowed, overwriting the saved return address on
    the stack. This allows an attacker to control the flow of execution and
    the opportunity to execute arbitrary code.

    Buffer Overflow Vulnerability in generate_distfile:
    The generate_distfile procedure is vulnerable to a buffer overflow
    vulnerability. generate_distfile is implemented as a C function, exported
    by db2dbappext.dll. It takes as its third parameter the name of a file.
    This parameter can be up to 255 characters long. One of the sub functions
    of generate_distfile takes the third parameter, the user supplied
    filename, and appends it to the directory where DB2 has been installed. It
    does this by creating a 264 byte buffer on the stack. The subfunction then
    calls sqloInstancePath() to get the install path for DB2. This returns
    C:\PROGRA~1\IBM\SQLLIB\DB2. \tmp\ is then appended to this.

    After \tmp\ is appended the user supplied filename is appended using a
    while loop that continues to copy data until a NULL terminator is found.
    Because the DB2 install path (C:\PROGRA~1\IBM\SQLLIB\DB2\tmp\) takes up
    some of the buffer, if the user has supplied a third parameter of 255
    bytes the stack based buffer is overflowed.

    However, once the buffer is overflowed, as well as overwriting the saved
    return address, a pointer is also overwritten. This pointer points to a
    buffer where the resulting full path should be copied to. This interrupts
    a straight return address overwrite exploit; however it can still easily
    be exploited in several ways. Due to the fact that the attacker "owns"
    the pointer to where the path is copied to, they can write arbitrary data
    to an arbitrary location allowing a full compromise. Once such method
    would be to overwrite the pointer to the Windows UnhandledExceptionFilter
    function; as access violations aren't handled, the UEF kicks in an as the
    attacker controls the UEF the flow of execution can be redirected by the
    attacker to arbitrary code.

     * Note - whilst the discussion has used Windows paths *nix versions of
    DB2 are also vulnerable.

    Vendor Status:
    IBM has written a patch and can be obtained with the latest FixPak.
     <http://www-306.ibm.com/software/data/db2/udb/support/downloadv8.html>
    DB2 v8.1
     <http://www-306.ibm.com/software/data/db2/udb/support/downloadv7.html>
    DB2 v7.x

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:nisr@nextgenss.com>
    NGSSoftware Insight Security Research.
    The original article can be found at:
    <http://www.ngssoftware.com/advisories/db223122004K.txt>
    http://www.ngssoftware.com/advisories/db223122004K.txt and
    <http://www.ngssoftware.com/advisories/db223122004L.txt>
    http://www.ngssoftware.com/advisories/db223122004L.txt

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