EUVD-2026-16128
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
3Description
When a challenge ACK is to be sent tcp_respond() constructs and sends the challenge ACK and consumes the mbuf that is passed in. When no challenge ACK should be sent the function returns and leaks the mbuf. If an attacker is either on path with an established TCP connection, or can themselves establish a TCP connection, to an affected FreeBSD machine, they can easily craft and send packets which meet the challenge ACK criteria and cause the FreeBSD host to leak an mbuf for each crafted packet in excess of the configured rate limit settings i.e. with default settings, crafted packets in excess of the first 5 sent within a 1s period will leak an mbuf. Technically, off-path attackers can also exploit this problem by guessing the IP addresses, TCP port numbers and in some cases the sequence numbers of established connections and spoofing packets towards a FreeBSD machine, but this is harder to do effectively.
Analysis
This vulnerability is a memory leak in FreeBSD's TCP stack where the tcp_respond() function fails to properly free allocated memory buffers (mbufs) when challenge ACKs are not sent in response to crafted packets. FreeBSD systems of all versions are affected. …
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Remediation
Within 7 days: Identify all affected systems and apply vendor patches promptly. Monitor vendor channels for patch availability.
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External POC / Exploit Code
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