CVE-2026-23016
inet: frags: drop fraglist conntrack references
Description
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 placed in defrag queue. Keep the nf_conn entry of the first (offset 0) skb so that reassembled skb retains nf_conn entry for sake of TX path. Note that fixes tag is incorrect; it points to the commit introducing the 'ip_defrag.sh reproducible problem': no need to backport this patch to every stable kernel.
INFO
Published Date :
Jan. 31, 2026, 12:16 p.m.
Last Modified :
Jan. 31, 2026, 12:16 p.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Affected Products
The following products are affected by CVE-2026-23016
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
Solution
- Modify defrag engine to drop nf_conn entries.
- Export kick_defer_list_purge() and call it.
- Add skb_has_frag_list() check to skb_attempt_defer_free().
- Drop nf_conn entries when placed in defrag queue.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-23016.
| URL | Resource |
|---|---|
| https://git.kernel.org/stable/c/088ca99dbb039c444c3ff987c5412a73f4f0cbf8 | |
| https://git.kernel.org/stable/c/2ef02ac38d3c17f34a00c4b267d961a8d4b45d1a |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-23016 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-23016
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-23016 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-23016 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jan. 31, 2026
Action Type Old Value New Value Added Description 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 placed in defrag queue. Keep the nf_conn entry of the first (offset 0) skb so that reassembled skb retains nf_conn entry for sake of TX path. Note that fixes tag is incorrect; it points to the commit introducing the 'ip_defrag.sh reproducible problem': no need to backport this patch to every stable kernel. Added Reference https://git.kernel.org/stable/c/088ca99dbb039c444c3ff987c5412a73f4f0cbf8 Added Reference https://git.kernel.org/stable/c/2ef02ac38d3c17f34a00c4b267d961a8d4b45d1a