CVE-2025-24934: SO_REUSEPORT_LB breaks connect(2) for UDP sockets

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-10-22 · updated 2026-10-19
Weakness: CWE-488

Description

Software which sets SO_REUSEPORT_LB on a socket and then connects it to a host will not directly observe any problems. However, due to its membership in a load-balancing group, that socket will receive packets originating from any host. This breaks the contract of the connect(2) and implied connect via sendto(2), and may leave the application vulnerable to spoofing attacks. The kernel failed to check the connection state of sockets when adding them to load-balancing groups. Furthermore, when looking up the destination socket for an incoming packet, the kernel will match a socket belonging to a load-balancing group even if it is connected, in violation of the contract that connected sockets are only supposed to receive packets originating from the connected host.

Affected products

FreeBSD: from 15.0-BETA2 before p1; from 14.3-RELEASE before p5; from 13.5-RELEASE before p6 — fixed in p1, p5, p6

How to fix

Upgrade to a fixed version: FreeBSD p1, p5, p6. Check the vendor advisory for mitigations.

References

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