Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-05-27T00:00:00 kernel: netfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation 7.0 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H CWE-367

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.

A flaw was found in the Linux kernel's netfilter (nfnetlink_queue) component. This vulnerability occurs when an application does not set the F_GSO capability flag and a Generic Segmentation Offload (GSO) packet with an unconfirmed netfilter connection (nf_conn) entry is received. Due to an incorrect order of checks, these packets are dropped instead of being queued. This can lead to a denial of service for affected UDP traffic.

Red Hat Enterprise Linux 10 Affected kernel Red Hat Enterprise Linux 6 Out of support scope kernel Red Hat Enterprise Linux 7 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel-rt Red Hat Enterprise Linux 8 Not affected kernel Red Hat Enterprise Linux 8 Not affected kernel-rt Red Hat Enterprise Linux 9 Affected kernel Red Hat Enterprise Linux 9 Affected kernel-rt https://www.cve.org/CVERecord?id=CVE-2026-45859 https://nvd.nist.gov/vuln/detail/CVE-2026-45859 https://lore.kernel.org/linux-cve-announce/2026052710-CVE-2026-45859-4440@gregkh/T