CVE-2026-23016: In the Linux kernel, the following vulnerability has been resolved: inet: frags: drop fraglist conntrack references Jakub added a warning in…

PriorityP421medium5.5CVSS 3.1

AVLACLPRLUINSUCNINAH

EPSS

0.13%

2.9th percentile

In the Linux kernel, the following vulnerability has been resolved: inet: frags: drop fraglist conntrack references Jakub added a warning in nf_conntrack_cleanup_net_list() to make debugging leaked skbs/conntrack references more obvious. syzbot reports this as triggering, and I can also reproduce this via ip_defrag.sh selftest: conntrack cleanup blocked for 60s WARNING: net/netfilter/nf_conntrack_core.c:2512 [..] conntrack clenups gets stuck because there are skbs with still hold nf_conn references via their frag_list. net.core.skb_defer_max=0 makes the hang disappear. Eric Dumazet points out that skb_release_head_state() doesn't follow the fraglist. ip_defrag.sh can only reproduce this problem since commit 6471658dc66c ("udp: use skb_attempt_defer_free()"), but AFAICS this problem could happen with TCP as well if pmtu discovery is off. The relevant problem path for udp is: 1. netns emits fragmented packets 2. nf_defrag_v6_hook reassembles them (in output hook) 3. reassembled skb is tracked (skb owns nf_conn reference) 4. ip6_output refragments 5. refragmented packets also own nf_conn reference (ip6_fragment calls ip6_copy_metadata()) 6. on input path, nf_defrag_v6_hook skips defragmentation: the fragments already have skb->nf_conn attached 7. skbs are reassembled via ipv6_frag_rcv() 8. skb_consume_udp -> skb_attempt_defer_free() -> skb ends up in pcpu freelist, but still has nf_conn reference. Possible solutions: 1 let defrag engine drop nf_conn entry, OR 2 export kick_defer_list_purge() and call it from the conntrack netns exit callback, OR 3 add skb_has_frag_list() check to skb_attempt_defer_free() 2 & 3 also solve ip_defrag.sh hang but share same drawback: Such reassembled skbs, queued to socket, can prevent conntrack module removal until userspace has consumed the packet. While both tcp and udp stack do call nf_reset_ct() before placing skb on socket queue, that function doesn't iterate frag_list skbs. Therefore drop nf_conn entries when they are p

Affected

9 ranges

Vendor	Product	Version range	Fixed in
debian	linux	< linux 6.18.8-1 (forky)	linux 6.18.8-1 (forky)
linux	linux	—	—
linux	linux	>= 6471658dc66c670580a7616e75f51b52917e7883 < 088ca99dbb039c444c3ff987c5412a73f4f0cbf8	088ca99dbb039c444c3ff987c5412a73f4f0cbf8
linux	linux	>= 6471658dc66c670580a7616e75f51b52917e7883 < 2ef02ac38d3c17f34a00c4b267d961a8d4b45d1a	2ef02ac38d3c17f34a00c4b267d961a8d4b45d1a
linux	linux_kernel	—	—
linux	linux_kernel	—	—
linux	linux_kernel	>= 0 < 6.18.8-1	6.18.8-1
linux	linux_kernel	>= 6.18.0 < 6.18.6	6.18.6
linux	linux_kernel	>= 6.18.1 < 6.18.6	6.18.6

CVSS provenance

nvdv3.15.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

osv5.5MEDIUM

vendor_debian5.5LOW

vendor_redhat5.5MEDIUM

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