FreeBSD VuXML: Documenting security issues in FreeBSD and the FreeBSD Ports Collection

FreeBSD -- pf incorrectly handles multiple IPv6 fragment headers

Affected packages
13.2 <= FreeBSD-kernel < 13.2_3
12.4 <= FreeBSD-kernel < 12.4_5


VuXML ID d35373ae-4d34-11ee-8e38-002590c1f29c
Discovery 2023-09-06
Entry 2023-09-07

Problem Description:

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.


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


CVE Name CVE-2023-4809
FreeBSD Advisory