TCP Vulnerability in FreeBSD Affects Network Integrity

CVE-2026-4247

What is CVE-2026-4247?

A vulnerability in FreeBSD allows attackers to exploit the tcp_respond() function, which handles challenge ACK packets. If an attacker can send crafted packets that meet specific challenge ACK criteria, it results in the leakage of mbufs—memory buffers used by the TCP stack. This leakage occurs when the FreeBSD host processes more than the configured rate limit of such packets, potentially compromising the host's memory integrity. While on-path attackers can easily execute this exploit, off-path attackers may also take advantage with more complex guessing techniques, making this a significant concern for network operators.

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