CVE-2023-4809 Information

Description

In pf packet processing with a ‘scrub fragment reassemble’ rule a packet containing multiple IPv6 fragment headers would be reassembled and then immediately processed. That is a packet with multiple fragment extension headers would not be recognized as the correct ultimate payload. Instead a packet with multiple IPv6 fragment headers would unexpectedly be interpreted as a fragmented packet rather than as whatever the real payload is.

As a result IPv6 fragments may bypass pf firewall rules written on the assumption all fragments have been reassembled and as a result be forwarded or processed by the host.

Reference

https://security.FreeBSD.org/advisories/FreeBSD-SA-23:10.pf.asc