What’s Vulnerable › Vulnerabilities

CVE-2023-4809: pf incorrectly handles multiple IPv6 fragment headers

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2023-09-06 · updated 2026-06-17
• Weakness: CWE-167

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.

Affected products

• FreeBSD: before 12.4; from 13.0 before 13.2; 12.4, 12.4-p1, 12.4-p2, 12.4-p3, 12.4-p4, 12.4-rc2-p1 (+4) — fixed in 12.4, 13.2

How to fix

Upgrade to a fixed version: FreeBSD 12.4, 13.2. Check the vendor advisory for mitigations.

References

• http://www.openwall.com/lists/oss-security/2023/09/08/5
• http://www.openwall.com/lists/oss-security/2023/09/08/6
• http://www.openwall.com/lists/oss-security/2023/09/08/7
• https://security.FreeBSD.org/advisories/FreeBSD-SA-23:10.pf.asc
• https://security.netapp.com/advisory/ntap-20231221-0009/
• http://www.openwall.com/lists/oss-security/2023/09/08/5
• http://www.openwall.com/lists/oss-security/2023/09/08/6
• http://www.openwall.com/lists/oss-security/2023/09/08/7
• https://security.FreeBSD.org/advisories/FreeBSD-SA-23:10.pf.asc
• https://security.netapp.com/advisory/ntap-20231221-0009/

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