CVE-2026-43116 (GCVE-0-2026-43116)
Vulnerability from cvelistv5
Published
2026-05-06 07:40
Modified
2026-08-05 12:26
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: ensure safe access to master conntrack Holding reference on the expectation is not sufficient, the master conntrack object can just go away, making exp->master invalid. To access exp->master safely: - Grab the nf_conntrack_expect_lock, this gets serialized with clean_from_lists() which also holds this lock when the master conntrack goes away. - Hold reference on master conntrack via nf_conntrack_find_get(). Not so easy since the master tuple to look up for the master conntrack is not available in the existing problematic paths. This patch goes for extending the nf_conntrack_expect_lock section to address this issue for simplicity, in the cases that are described below this is just slightly extending the lock section. The add expectation command already holds a reference to the master conntrack from ctnetlink_create_expect(). However, the delete expectation command needs to grab the spinlock before looking up for the expectation. Expand the existing spinlock section to address this to cover the expectation lookup. Note that, the nf_ct_expect_iterate_net() calls already grabs the spinlock while iterating over the expectation table, which is correct. The get expectation command needs to grab the spinlock to ensure master conntrack does not go away. This also expands the existing spinlock section to cover the expectation lookup too. I needed to move the netlink skb allocation out of the spinlock to keep it GFP_KERNEL. For the expectation events, the IPEXP_DESTROY event is already delivered under the spinlock, just move the delivery of IPEXP_NEW under the spinlock too because the master conntrack event cache is reached through exp->master. While at it, add lockdep notations to help identify what codepaths need to grab the spinlock.
References
Impacted products
Vendor Product Version
Linux Linux Version: c1d10adb4a521de5760112853f42aaeefcec96eb
Version: c1d10adb4a521de5760112853f42aaeefcec96eb
Version: c1d10adb4a521de5760112853f42aaeefcec96eb
Version: c1d10adb4a521de5760112853f42aaeefcec96eb
Version: c1d10adb4a521de5760112853f42aaeefcec96eb
Version: c1d10adb4a521de5760112853f42aaeefcec96eb
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/net/netfilter/nf_conntrack_core.h",
            "net/netfilter/nf_conntrack_ecache.c",
            "net/netfilter/nf_conntrack_expect.c",
            "net/netfilter/nf_conntrack_netlink.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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          "versions": [
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        },
        {
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          "product": "Linux",
          "programFiles": [
            "include/net/netfilter/nf_conntrack_core.h",
            "net/netfilter/nf_conntrack_ecache.c",
            "net/netfilter/nf_conntrack_expect.c",
            "net/netfilter/nf_conntrack_netlink.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "2.6.16"
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              "version": "0",
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              "version": "6.1.176",
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              "status": "unaffected",
              "version": "6.12.94",
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            },
            {
              "lessThanOrEqual": "6.18.*",
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              "version": "6.18.24",
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            },
            {
              "lessThanOrEqual": "6.19.*",
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              "version": "6.19.14",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.0",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.176",
                  "versionStartIncluding": "2.6.16",
                  "vulnerable": true
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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\nnetfilter: ctnetlink: ensure safe access to master conntrack\n\nHolding reference on the expectation is not sufficient, the master\nconntrack object can just go away, making exp-\u003emaster invalid.\n\nTo access exp-\u003emaster safely:\n\n- Grab the nf_conntrack_expect_lock, this gets serialized with\n  clean_from_lists() which also holds this lock when the master\n  conntrack goes away.\n\n- Hold reference on master conntrack via nf_conntrack_find_get().\n  Not so easy since the master tuple to look up for the master conntrack\n  is not available in the existing problematic paths.\n\nThis patch goes for extending the nf_conntrack_expect_lock section\nto address this issue for simplicity, in the cases that are described\nbelow this is just slightly extending the lock section.\n\nThe add expectation command already holds a reference to the master\nconntrack from ctnetlink_create_expect().\n\nHowever, the delete expectation command needs to grab the spinlock\nbefore looking up for the expectation. Expand the existing spinlock\nsection to address this to cover the expectation lookup. Note that,\nthe nf_ct_expect_iterate_net() calls already grabs the spinlock while\niterating over the expectation table, which is correct.\n\nThe get expectation command needs to grab the spinlock to ensure master\nconntrack does not go away. This also expands the existing spinlock\nsection to cover the expectation lookup too. I needed to move the\nnetlink skb allocation out of the spinlock to keep it GFP_KERNEL.\n\nFor the expectation events, the IPEXP_DESTROY event is already delivered\nunder the spinlock, just move the delivery of IPEXP_NEW under the\nspinlock too because the master conntrack event cache is reached through\nexp-\u003emaster.\n\nWhile at it, add lockdep notations to help identify what codepaths need\nto grab the spinlock."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The vulnerable ctnetlink expectation operations are reached through NETLINK_NETFILTER messages from local userspace, not directly by remote packets.\nAC:L - The race is between attacker-driven ctnetlink expectation lookup/dump/delete and attacker-driven master conntrack deletion or timeout, so the attacker can create and retry both sides.\nPR:L - nfnetlink requires CAP_NET_ADMIN in the target network namespace, and an unprivileged local user can reasonably obtain that via a user plus network namespace on affected deployments.\nUI:N - No victim action is required after the attacker can send the netlink requests.\nS:U - This is a kernel memory safety issue within the same host security authority and does not cross a VM, IOMMU, or similar scope boundary.\nC:H - The bug is a use-after-free of the master struct nf_conn reachable from a retained expectation, and kernel UAFs can be leveraged for disclosure of sensitive kernel memory.\nI:H - The stale master pointer is kernel heap memory corruption/use-after-free, which is defensibly exploitable for control-flow or data modification with heap grooming.\nA:H - Even without full exploitation, dereferencing the freed master conntrack can trigger a kernel oops or panic."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:26:02.836Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/9e1196d27ef496f404c76f7a9d03761142d991c4"
        },
        {
          "url": "https://git.kernel.org/stable/c/5e1c1d22268ae710c238342c8030c21daf298168"
        },
        {
          "url": "https://git.kernel.org/stable/c/d52fa1fa7440676b8c238037a050ab008c22737f"
        },
        {
          "url": "https://git.kernel.org/stable/c/f338ced0473849c9f6ed0b77ca99f1aab5826787"
        },
        {
          "url": "https://git.kernel.org/stable/c/497f99b26fffdc5635706d1b4811f1ed8ee21a5b"
        },
        {
          "url": "https://git.kernel.org/stable/c/bffcaad9afdfe45d7fc777397d3b83c1e3ebffe5"
        }
      ],
      "title": "netfilter: ctnetlink: ensure safe access to master conntrack",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-43116",
    "datePublished": "2026-05-06T07:40:41.185Z",
    "dateReserved": "2026-05-01T14:12:55.986Z",
    "dateUpdated": "2026-08-05T12:26:02.836Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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