CVE-2024-6640: pf incorrectly matches different ICMPv6 states in the state table

Severity: medium (CVSS 6.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-08-12 · updated 2026-06-17
Weakness: CWE-276

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.

Affected products

FreeBSD: from 14.1-RELEASE before p3; from 14.0-RELEASE before p9; from 13.3-RELEASE before p5 — fixed in p3, p5, p9

How to fix

Upgrade to a fixed version: FreeBSD p3, p5, p9. Check the vendor advisory for mitigations.

References

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