SB2026101491 - Remote DoS in FreeBSD tcp_rack

Description

This security bulletin contains information about 1 vulnerability.

1) Out-of-bounds write (CVE-ID: CVE-2026-101307)

CWE-ID: CWE-787 - Out-of-bounds write

CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to an out-of-bounds write in the RACK stack's path capacity measurement (PCM) module when a 16-bit allocation counter wraps to zero during sample array expansion. A remote attacker can send a sufficient number of ACKs on an established TCP connection to cause a denial of service.

Exploitation requires the tcp_rack.ko kernel module to be loaded and the target connection to use the RACK stack.

Remediation

Install update from vendor's website.

References

• https://www.freebsd.org/security/advisories/FreeBSD-SA-26:70.tcp.asc
• https://cgit.freebsd.org/src/commit/?id=5dd20a06fe9e