CVE-2024-6640: pf incorrectly matches different ICMPv6 states in the state table
Description
In ICMPv6 Neighbor Discovery (ND), the ID is always 0. When pf is configured to allow ND and block incoming Echo Requests, a crafted Echo Request packet after a Neighbor Solicitation (NS) can trigger an Echo Reply. The packet has to come from the same host as the NS and have a zero as identifier to match the state created by the Neighbor Discovery and allow replies to be generated.
ICMPv6 packets with identifier value of zero bypass firewall rules written on the assumption that the incoming packets are going to create a state in the state table.
Classification
CVE ID: CVE-2024-6640
CVSS Base Severity: LOW
CVSS Base Score: 0.0
Affected Products
Vendor: FreeBSD
Product: FreeBSD
Exploit Prediction Scoring System (EPSS)
EPSS Score: 0.04% (probability of being exploited)
EPSS Percentile: 11.44% (scored less or equal to compared to others)
EPSS Date: 2025-02-03 (when was this score calculated)