Is CVE-2026-101307 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-101307 being exploited in the wild.

How severe is CVE-2026-101307?

Critical severity, with a CVSS score of 9.1, published 15 October 2026.

How is CVE-2026-101307 attacked?

It is attacked over the network, in an operating system.

Am I affected by CVE-2026-101307?

Check whether you run Freebsd at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-101307: FreeBSD RACK stack buffer overflow in tcp_rack

CVE-2026-101307 · Severity: critical · CVSS 9.1 · Published 2026-10-15

The RACK TCP stack module in FreeBSD contains a buffer overflow in its path capacity measurement component. A remote attacker can trigger the vulnerability by sending specially crafted TCP acknowledgments on an established connection, causing approximately 512 KB of kernel heap corruption that may result in a system crash. This affects systems that have the tcp_rack kernel module loaded.

Technologies: Freebsd. Vendors: Freebsd.

Quick answers

Is CVE-2026-101307 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-101307 being exploited in the wild.
How severe is CVE-2026-101307?: Critical severity, with a CVSS score of 9.1, published 15 October 2026.
Which products and versions are affected?: Freebsd 15.1.
Is there a fix for CVE-2026-101307?: Yes: fixed in FreeBSD 15.1-RELEASE-p5, stable/15 as of 2026-10-14. Until then: Unload the tcp_rack kernel module on systems where the RACK stack is not required. Run 'kldstat -m tcp_rack' to verify if the module is loaded. The tcpsso(8) utility can migrate existing TCP connections to an alternative TCP stack.</anigation> <parameter name="timeline">[{"kind":"disclosed","at":"2026-10-14"},{"kind":"patched","at":"2026-10-14"}] Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-101307 attacked?: It is attacked over the network, in an operating system.
Am I affected by CVE-2026-101307?: Check whether you run Freebsd at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

Fixed in: FreeBSD 15.1-RELEASE-p5, stable/15 as of 2026-10-14

Unload the tcp_rack kernel module on systems where the RACK stack is not required. Run 'kldstat -m tcp_rack' to verify if the module is loaded. The tcpsso(8) utility can migrate existing TCP connections to an alternative TCP stack.</anigation> <parameter name="timeline">[{"kind":"disclosed","at":"2026-10-14"},{"kind":"patched","at":"2026-10-14"}]

Technical details

The vulnerability exists in the RACK stack's PCM sample array expansion logic, which uses a 16-bit allocation counter that doubles to grow the array. Repeated doublings cause integer overflow and wraparound to zero, resulting in a vastly undersized heap allocation followed by an out-of-bounds copy of the original samples. A remote peer with an established TCP connection can trigger repeated array expansions by sending sufficient ACKs, leading to kernel heap corruption and potential denial of service.

Affected products

FreeBSD FreeBSD 15.1

References

https://security.freebsd.org/advisories/FreeBSD-SA-26:70.tcp.asc

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