Vulnerability-Lookup

GHSA-8H8Q-4WVG-MHGM

Vulnerability from github – Published: 2026-01-31 12:30 – Updated: 2026-01-31 12:30

Details

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.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-23016"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-01-31T12:16:04Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ninet: frags: drop fraglist conntrack references\n\nJakub added a warning in nf_conntrack_cleanup_net_list() to make debugging\nleaked skbs/conntrack references more obvious.\n\nsyzbot reports this as triggering, and I can also reproduce this via\nip_defrag.sh selftest:\n\n conntrack cleanup blocked for 60s\n WARNING: net/netfilter/nf_conntrack_core.c:2512\n [..]\n\nconntrack clenups gets stuck because there are skbs with still hold nf_conn\nreferences via their frag_list.\n\n   net.core.skb_defer_max=0 makes the hang disappear.\n\nEric Dumazet points out that skb_release_head_state() doesn\u0027t follow the\nfraglist.\n\nip_defrag.sh can only reproduce this problem since\ncommit 6471658dc66c (\"udp: use skb_attempt_defer_free()\"), but AFAICS this\nproblem could happen with TCP as well if pmtu discovery is off.\n\nThe relevant problem path for udp is:\n1. netns emits fragmented packets\n2. nf_defrag_v6_hook reassembles them (in output hook)\n3. reassembled skb is tracked (skb owns nf_conn reference)\n4. ip6_output refragments\n5. refragmented packets also own nf_conn reference (ip6_fragment\n   calls ip6_copy_metadata())\n6. on input path, nf_defrag_v6_hook skips defragmentation: the\n   fragments already have skb-\u003enf_conn attached\n7. skbs are reassembled via ipv6_frag_rcv()\n8. skb_consume_udp -\u003e skb_attempt_defer_free() -\u003e skb ends up\n   in pcpu freelist, but still has nf_conn reference.\n\nPossible solutions:\n 1 let defrag engine drop nf_conn entry, OR\n 2 export kick_defer_list_purge() and call it from the conntrack\n   netns exit callback, OR\n 3 add skb_has_frag_list() check to skb_attempt_defer_free()\n\n2 \u0026 3 also solve ip_defrag.sh hang but share same drawback:\n\nSuch reassembled skbs, queued to socket, can prevent conntrack module\nremoval until userspace has consumed the packet. While both tcp and udp\nstack do call nf_reset_ct() before placing skb on socket queue, that\nfunction doesn\u0027t iterate frag_list skbs.\n\nTherefore drop nf_conn entries when they are placed in defrag queue.\nKeep the nf_conn entry of the first (offset 0) skb so that reassembled\nskb retains nf_conn entry for sake of TX path.\n\nNote that fixes tag is incorrect; it points to the commit introducing the\n\u0027ip_defrag.sh reproducible problem\u0027: no need to backport this patch to\nevery stable kernel.",
  "id": "GHSA-8h8q-4wvg-mhgm",
  "modified": "2026-01-31T12:30:12Z",
  "published": "2026-01-31T12:30:12Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23016"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/088ca99dbb039c444c3ff987c5412a73f4f0cbf8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2ef02ac38d3c17f34a00c4b267d961a8d4b45d1a"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-23016 (GCVE-0-2026-23016)

Vulnerability from cvelistv5 – Published: 2026-01-31 11:38 – Updated: 2026-02-09 08:37

Title

inet: frags: drop fraglist conntrack references

Summary

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.

Severity ?

No CVSS data available.

Assigner

Linux

References

URL

Tags

	https://git.kernel.org/stable/c/088ca99dbb039c444…
	https://git.kernel.org/stable/c/2ef02ac38d3c17f34…

Impacted products

Vendor

Product

Version

Linux

Affected: 6471658dc66c670580a7616e75f51b52917e7883 , < 088ca99dbb039c444c3ff987c5412a73f4f0cbf8 (git)
Affected: 6471658dc66c670580a7616e75f51b52917e7883 , < 2ef02ac38d3c17f34a00c4b267d961a8d4b45d1a (git)

Linux

Affected: 6.18
Unaffected: 0 , < 6.18 (semver)
Unaffected: 6.18.6 , ≤ 6.18.* (semver)
Unaffected: 6.19 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/inet_fragment.c"
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "088ca99dbb039c444c3ff987c5412a73f4f0cbf8",
              "status": "affected",
              "version": "6471658dc66c670580a7616e75f51b52917e7883",
              "versionType": "git"
            },
            {
              "lessThan": "2ef02ac38d3c17f34a00c4b267d961a8d4b45d1a",
              "status": "affected",
              "version": "6471658dc66c670580a7616e75f51b52917e7883",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/inet_fragment.c"
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          "vendor": "Linux",
          "versions": [
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              "status": "unaffected",
              "version": "0",
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              "status": "unaffected",
              "version": "6.18.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.19",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.6",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.19",
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                }
              ],
              "negate": false,
              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ninet: frags: drop fraglist conntrack references\n\nJakub added a warning in nf_conntrack_cleanup_net_list() to make debugging\nleaked skbs/conntrack references more obvious.\n\nsyzbot reports this as triggering, and I can also reproduce this via\nip_defrag.sh selftest:\n\n conntrack cleanup blocked for 60s\n WARNING: net/netfilter/nf_conntrack_core.c:2512\n [..]\n\nconntrack clenups gets stuck because there are skbs with still hold nf_conn\nreferences via their frag_list.\n\n   net.core.skb_defer_max=0 makes the hang disappear.\n\nEric Dumazet points out that skb_release_head_state() doesn\u0027t follow the\nfraglist.\n\nip_defrag.sh can only reproduce this problem since\ncommit 6471658dc66c (\"udp: use skb_attempt_defer_free()\"), but AFAICS this\nproblem could happen with TCP as well if pmtu discovery is off.\n\nThe relevant problem path for udp is:\n1. netns emits fragmented packets\n2. nf_defrag_v6_hook reassembles them (in output hook)\n3. reassembled skb is tracked (skb owns nf_conn reference)\n4. ip6_output refragments\n5. refragmented packets also own nf_conn reference (ip6_fragment\n   calls ip6_copy_metadata())\n6. on input path, nf_defrag_v6_hook skips defragmentation: the\n   fragments already have skb-\u003enf_conn attached\n7. skbs are reassembled via ipv6_frag_rcv()\n8. skb_consume_udp -\u003e skb_attempt_defer_free() -\u003e skb ends up\n   in pcpu freelist, but still has nf_conn reference.\n\nPossible solutions:\n 1 let defrag engine drop nf_conn entry, OR\n 2 export kick_defer_list_purge() and call it from the conntrack\n   netns exit callback, OR\n 3 add skb_has_frag_list() check to skb_attempt_defer_free()\n\n2 \u0026 3 also solve ip_defrag.sh hang but share same drawback:\n\nSuch reassembled skbs, queued to socket, can prevent conntrack module\nremoval until userspace has consumed the packet. While both tcp and udp\nstack do call nf_reset_ct() before placing skb on socket queue, that\nfunction doesn\u0027t iterate frag_list skbs.\n\nTherefore drop nf_conn entries when they are placed in defrag queue.\nKeep the nf_conn entry of the first (offset 0) skb so that reassembled\nskb retains nf_conn entry for sake of TX path.\n\nNote that fixes tag is incorrect; it points to the commit introducing the\n\u0027ip_defrag.sh reproducible problem\u0027: no need to backport this patch to\nevery stable kernel."
        }
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        "dateUpdated": "2026-02-09T08:37:09.768Z",
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          "url": "https://git.kernel.org/stable/c/2ef02ac38d3c17f34a00c4b267d961a8d4b45d1a"
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      ],
      "title": "inet: frags: drop fraglist conntrack references",
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-23016",
    "datePublished": "2026-01-31T11:38:59.578Z",
    "dateReserved": "2026-01-13T15:37:45.940Z",
    "dateUpdated": "2026-02-09T08:37:09.768Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
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}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-8H8Q-4WVG-MHGM

CVE-2026-23016 (GCVE-0-2026-23016)

Tags

Sightings

Nomenclature