CVE-2026-45859

Summary

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 Software

Weaknesses

References

• https://git.kernel.org/stable/c/79b713ef4261a8ead96af4703f89d0b5f25532e2
• https://git.kernel.org/stable/c/23901aa6b8a2f294c4b774436b4691f3ff863a8f
• https://git.kernel.org/stable/c/b740e7ddd7ca0dbfeafca3f5e52717206cf28524
• https://git.kernel.org/stable/c/207b3ebacb6113acaaec0d171d5307032c690004

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