CVE-2026-31418: netfilter: ipset: drop logically empty buckets in mtype_del

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-13 · updated 2026-10-15

Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: ipset: drop logically empty buckets in mtype_del mtype_del() counts empty slots below n->pos in k, but it only drops the bucket when both n->pos and k are zero. This misses buckets whose live entries have all been removed while n->pos still points past deleted slots. Treat a bucket as empty when all positions below n->pos are unused and release it directly instead of shrinking it further.

Affected products

Linux kernel: from 5.4.24 before 5.5; from 5.5.8 before 5.6; from 5.6.1 before 5.10.253; from 5.11 before 5.15.203; from 5.16 before 6.1.168; from 6.2 before 6.6.134 — fixed in 5.10.253, 5.15.203, 5.5, 5.6, 6.1.168, 6.12.81

How to fix

Upgrade to a fixed version: Linux kernel 5.10.253, 5.15.203, 5.5, 5.6. Check the vendor advisory for mitigations.

References

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