CVE-2026-45859: netfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-27 · updated 2026-10-30
Weakness: CWE-400

Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation Ulrich reports a regression with nfqueue: If an application did not set the 'F_GSO' capability flag and a gso packet with an unconfirmed nf_conn entry is received all packets are now dropped instead of queued, because the check happens after skb_gso_segment(). In that case, we did have exclusive ownership of the skb and its associated conntrack entry. The elevated use count is due to skb_clone happening via skb_gso_segment(). Move the check so that its peformed vs. the aggregated packet. Then, annotate the individual segments except the first one so we can do a 2nd check at reinject time. For the normal case, where userspace does in-order reinjects, this avoids packet drops: first reinjected segment continues traversal and confirms entry, remaining segments observe the confirmed entry. While at it, simplify nf_ct_drop_unconfirmed(): We only care about unconfirmed entries with a refcnt > 1, there is no need to special-case dying entries. This only happens with UDP. With TCP, the only unconfirmed packet will be the TCP SYN, those aren't aggregated by GRO. Next patch adds a udpgro test case to cover this scenario.

Affected products

Linux kernel: from 5.15.166 before 5.16; from 6.1.107 before 6.2; from 6.6.48 before 6.7; from 6.10.7 before 6.11; from 6.11.1 before 6.12.75; from 6.13 before 6.18.14 — fixed in 5.16, 6.2, 6.7, 6.11, 6.12.75, 6.18.14
Linux: from 6.1.107 before 6.1.191; from 6.6.48 before 6.6.160; from 5.15.166 before 5.16; from 6.10.7 before 6.11 — fixed in 6.1.191, 6.6.160, 5.16, 6.11

How to fix

Upgrade to a fixed version: Linux kernel 5.16, 6.2, 6.7, 6.11; Linux 6.1.191, 6.6.160, 5.16, 6.11. Check the vendor advisory for mitigations.

References

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