CVE-2025-38721 (GCVE-0-2025-38721)

Vulnerability from cvelistv5 – Published: 2025-09-04 15:33 – Updated: 2026-10-15 01:07
VLAI
Title
netfilter: ctnetlink: fix refcount leak on table dump
Summary
In the Linux kernel, the following vulnerability has been resolved: netfilter: ctnetlink: fix refcount leak on table dump There is a reference count leak in ctnetlink_dump_table(): if (res < 0) { nf_conntrack_get(&ct->ct_general); // HERE cb->args[1] = (unsigned long)ct; ... While its very unlikely, its possible that ct == last. If this happens, then the refcount of ct was already incremented. This 2nd increment is never undone. This prevents the conntrack object from being released, which in turn keeps prevents cnet->count from dropping back to 0. This will then block the netns dismantle (or conntrack rmmod) as nf_conntrack_cleanup_net_list() will wait forever. This can be reproduced by running conntrack_resize.sh selftest in a loop. It takes ~20 minutes for me on a preemptible kernel on average before I see a runaway kworker spinning in nf_conntrack_cleanup_net_list. One fix would to change this to: if (res < 0) { if (ct != last) nf_conntrack_get(&ct->ct_general); But this reference counting isn't needed in the first place. We can just store a cookie value instead. A followup patch will do the same for ctnetlink_exp_dump_table, it looks to me as if this has the same problem and like ctnetlink_dump_table, we only need a 'skip hint', not the actual object so we can apply the same cookie strategy there as well.
Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7063 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: d205dc40798d97d63ad348bfaf7394f445d152d4 , < 586892e341fbf698e7cbaca293e1353957db725a (git)
Affected: d205dc40798d97d63ad348bfaf7394f445d152d4 , < 962518c6ca9f9a13df099cafa429f72f68ad61f0 (git)
Affected: d205dc40798d97d63ad348bfaf7394f445d152d4 , < 19b909a4b1452fb97e477d2f08b97f8d04095619 (git)
Affected: d205dc40798d97d63ad348bfaf7394f445d152d4 , < 41462f4cfc583513833f87f9ee55d12da651a7e3 (git)
Affected: d205dc40798d97d63ad348bfaf7394f445d152d4 , < 30cf811058552b8cd0e98dff677ef3f89d6d34ce (git)
Affected: d205dc40798d97d63ad348bfaf7394f445d152d4 , < a2cb4df7872de069f809de2f076ec8e54d649fe3 (git)
Affected: d205dc40798d97d63ad348bfaf7394f445d152d4 , < e14f72aa66c029db106921d621edcedef68e065b (git)
Affected: d205dc40798d97d63ad348bfaf7394f445d152d4 , < a62d6aa3f31f216b637a4c71b7a8bfc7c57f049b (git)
Affected: d205dc40798d97d63ad348bfaf7394f445d152d4 , < de788b2e6227462b6dcd0e07474e72c089008f74 (git)
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Linux Linux Affected: 2.6.18
Unaffected: 0 , < 2.6.18 (semver)
Unaffected: 5.4.297 , ≤ 5.4.* (semver)
Unaffected: 5.10.241 , ≤ 5.10.* (semver)
Unaffected: 5.15.190 , ≤ 5.15.* (semver)
Unaffected: 6.1.149 , ≤ 6.1.* (semver)
Unaffected: 6.6.103 , ≤ 6.6.* (semver)
Unaffected: 6.12.43 , ≤ 6.12.* (semver)
Unaffected: 6.15.11 , ≤ 6.15.* (semver)
Unaffected: 6.16.2 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
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Siemens SIMATIC CN 4100 Affected: 0 , < V5.0 (custom)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.7 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Affected: V3.1.7 , < * (custom)
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Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
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Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
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Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.7 , < * (custom)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: ctnetlink: fix refcount leak on table dump\n\nThere is a reference count leak in ctnetlink_dump_table():\n      if (res \u003c 0) {\n                nf_conntrack_get(\u0026ct-\u003ect_general); // HERE\n                cb-\u003eargs[1] = (unsigned long)ct;\n                ...\n\nWhile its very unlikely, its possible that ct == last.\nIf this happens, then the refcount of ct was already incremented.\nThis 2nd increment is never undone.\n\nThis prevents the conntrack object from being released, which in turn\nkeeps prevents cnet-\u003ecount from dropping back to 0.\n\nThis will then block the netns dismantle (or conntrack rmmod) as\nnf_conntrack_cleanup_net_list() will wait forever.\n\nThis can be reproduced by running conntrack_resize.sh selftest in a loop.\nIt takes ~20 minutes for me on a preemptible kernel on average before\nI see a runaway kworker spinning in nf_conntrack_cleanup_net_list.\n\nOne fix would to change this to:\n        if (res \u003c 0) {\n\t\tif (ct != last)\n\t                nf_conntrack_get(\u0026ct-\u003ect_general);\n\nBut this reference counting isn\u0027t needed in the first place.\nWe can just store a cookie value instead.\n\nA followup patch will do the same for ctnetlink_exp_dump_table,\nit looks to me as if this has the same problem and like\nctnetlink_dump_table, we only need a \u0027skip hint\u0027, not the actual\nobject so we can apply the same cookie strategy there as well."
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: ctnetlink: fix refcount leak on table dump\n\nThere is a reference count leak in ctnetlink_dump_table():\n      if (res \u003c 0) {\n                nf_conntrack_get(\u0026ct-\u003ect_general); // HERE\n                cb-\u003eargs[1] = (unsigned long)ct;\n                ...\n\nWhile its very unlikely, its possible that ct == last.\nIf this happens, then the refcount of ct was already incremented.\nThis 2nd increment is never undone.\n\nThis prevents the conntrack object from being released, which in turn\nkeeps prevents cnet-\u003ecount from dropping back to 0.\n\nThis will then block the netns dismantle (or conntrack rmmod) as\nnf_conntrack_cleanup_net_list() will wait forever.\n\nThis can be reproduced by running conntrack_resize.sh selftest in a loop.\nIt takes ~20 minutes for me on a preemptible kernel on average before\nI see a runaway kworker spinning in nf_conntrack_cleanup_net_list.\n\nOne fix would to change this to:\n        if (res \u003c 0) {\n\t\tif (ct != last)\n\t                nf_conntrack_get(\u0026ct-\u003ect_general);\n\nBut this reference counting isn\u0027t needed in the first place.\nWe can just store a cookie value instead.\n\nA followup patch will do the same for ctnetlink_exp_dump_table,\nit looks to me as if this has the same problem and like\nctnetlink_dump_table, we only need a \u0027skip hint\u0027, not the actual\nobject so we can apply the same cookie strategy there as well."
          },
          {
            "lang": "es",
            "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nnetfilter: ctnetlink: correcci\u00f3n de fuga de contador de referencias en el volcado de tabla\n\nHay una fuga de contador de referencias en ctnetlink_dump_table():\n      if (res \u003c 0) {\n                nf_conntrack_get(\u0026ct-\u003ect_general); // AQU\u00cd\n                cb-\u003eargs[1] = (unsigned long)ct;\n                ...\n\nAunque es muy improbable, es posible que ct == last.\nSi esto ocurre, entonces el contador de referencias de ct ya se hab\u00eda incrementado.\nEste segundo incremento nunca se deshace.\n\nEsto evita que el objeto conntrack sea liberado, lo que a su vez\nimpide que cnet-\u003ecount vuelva a 0.\n\nEsto entonces bloquear\u00e1 el desmantelamiento de netns (o rmmod de conntrack) ya que\nnf_conntrack_cleanup_net_list() esperar\u00e1 indefinidamente.\n\nEsto puede reproducirse ejecutando la autoprueba conntrack_resize.sh en un bucle.\nMe lleva ~20 minutos en un kernel preemptivo en promedio antes de que\nvea un kworker descontrolado girando en nf_conntrack_cleanup_net_list.\n\nUna soluci\u00f3n ser\u00eda cambiar esto a:\n        if (res \u003c 0) {\n\t\tif (ct != last)\n\t                nf_conntrack_get(\u0026ct-\u003ect_general);\n\nPero este conteo de referencias no es necesario en primer lugar.\nPodemos simplemente almacenar un valor de cookie en su lugar.\n\nUn parche de seguimiento har\u00e1 lo mismo para ctnetlink_exp_dump_table,\nme parece que esto tiene el mismo problema y al igual que\nctnetlink_dump_table, solo necesitamos una \u0027pista de salto\u0027, no el objeto real,\nas\u00ed que podemos aplicar la misma estrategia de cookie all\u00ed tambi\u00e9n."
          }
        ],
        "id": "CVE-2025-38721",
        "lastModified": "2026-10-19T21:10:00.160",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 5.5,
                "baseSeverity": "MEDIUM",
                "confidentialityImpact": "NONE",
                "integrityImpact": "NONE",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 1.8,
              "impactScore": 3.6,
              "source": "nvd@nist.gov",
              "type": "Primary"
            }
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        "published": "2025-09-04T16:15:41.843",
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            "tags": [
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        "vulnStatus": "Modified",
        "weaknesses": [
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              {
                "lang": "en",
                "value": "NVD-CWE-Other"
              }
            ],
            "source": "nvd@nist.gov",
            "type": "Primary"
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    },
    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-06-30T10:36:13+00:00",
      "cve": "CVE-2025-38721",
      "id": "CVE-2025-38721",
      "initial_release_date": "2025-09-04T00:00:00+00:00",
      "product_status:known_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: netfilter: ctnetlink: fix refcount leak on table dump",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-38721.json",
      "version": "3"
    }
  }
}



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Tags
Taxonomy of the tags.




Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.

Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

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.
Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

JSON

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    Related by attack behaviour

    Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.