CVE-2026-31503

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

udp: Fix wildcard bind conflict check when using hash2

When binding a udp_sock to a local address and port, UDP uses

two hashes (udptable->hash and udptable->hash2) for collision

detection. The current code switches to "hash2" when

hslot->count > 10.

"hash2" is keyed by local address and local port.

"hash" is keyed by local port only.

The issue can be shown in the following bind sequence (pseudo code):

bind(fd1, "[fd00::1]:8888")

bind(fd2, "[fd00::2]:8888")

bind(fd3, "[fd00::3]:8888")

bind(fd4, "[fd00::4]:8888")

bind(fd5, "[fd00::5]:8888")

bind(fd6, "[fd00::6]:8888")

bind(fd7, "[fd00::7]:8888")

bind(fd8, "[fd00::8]:8888")

bind(fd9, "[fd00::9]:8888")

bind(fd10, "[fd00::10]:8888")

/* Correctly return -EADDRINUSE because "hash" is used

* instead of "hash2". udp_lib_lport_inuse() detects the

* conflict.

*/

bind(fail_fd, "[::]:8888")

/* After one more socket is bound to "[fd00::11]:8888",

* hslot->count

Remediation

Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected Products

References