FreeBSD ppp deny_incoming Vulnerability

ppp is a utility used for handling point-to-point network connections in unix systems. The FreeBSD version of ppp also facilitates NAT, or network address translation for proxied communication between networks.

There is an option in ppp, "nat deny_incoming" which can be used as a broad, simple "firewall rule". It tells the machine performing nat not to let anything pass through the gateway that is not part of an existing nat session. Code was added to this functonality to permit certain types of data through the nat gateway that introduced a bug resulting in all traffic passing through, despite the "deny_incoming" directive.

This may result in a violation of security policy and can lead to attacks on the internal network behind the gateway.


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