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CVE-2026-74621

Estado: RecibidaAlta (7.5)—

In the Linux kernel, the following vulnerability has been resolved:

net/sched: act_ct: fix sk_buff leak when the header checks reject a packet

tcf_ct_handle_fragments() runs its header sanity checks before handing anything to the defragmentation engine:

tcf_ct_ipv4_is_fragment() returns -EINVAL or -ENOMEM; tcf_ct_ipv6_is_fragment() adds -EPROTO when ipv6_find_hdr() fails. None of them frees or queues the skb, so on that path the caller still owns it.

tcf_ct_act() however funnels every non-zero return into the ownership-transfer exit:

TC_ACT_CONSUMED means the action took ownership of the skb, so no caller frees it - sch_handle_ingress(), sch_handle_egress() and tcf_qevent_handle() all deliberately skip the free for that verdict.

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The skb is therefore orphaned: one sk_buff plus its data buffer is leaked per malformed packet, unbounded. Note the drop counter is already incremented for these errors, so the statistics claim a drop that never happens.

Three different ownership states reach out_frag: today - the skb may be queued by the defrag engine (-EINPROGRESS), already freed by nf_ct_handle_fragments(), or still owned by us. Tell the caller which of those it is, and free the packet ourselves in the last case, which restores the TC_ACT_SHOT behaviour that predated the Fixes: commit.

Reproduced on v7.2-rc6 with a 54-byte frame carrying a 40-byte IPv6 header with nexthdr = 0 (hop-by-hop) and nothing after it, on a clsact ingress chain with "action ct". kmemleak reports one leaked 232-byte skbuff_head_cache object plus its 704-byte data buffer per packet; with this patch it reports none.

Detalles técnicos trazas, registros y código del informe original
	if (family == NFPROTO_IPV4)
		err = tcf_ct_ipv4_is_fragment(skb, &frag);
	else
		err = tcf_ct_ipv6_is_fragment(skb, &frag);
	if (err || !frag)
		return err;

	err = tcf_ct_handle_fragments(net, skb, family, p->zone, &defrag);
	if (err)
		goto out_frag;
	...
out_frag:
	if (err != -EINPROGRESS)
		tcf_action_inc_drop_qstats(&c->common);
	return TC_ACT_CONSUMED;

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vulnerabilidad de DoS remota en el kernel Linux (AV:N, PR:N) mediante paquetes IPv4/IPv6 malformados que causan fuga de memoria (skb_buff leak), permitiendo consumo unbounded de recursos sin autenticación.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Filter Network TrafficVulnerability ScanningPrivileged Account ManagementNetwork SegmentationLimit Access to Resource Over NetworkApplication Isolation and Sandboxing

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux KernelAI

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-74621",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.5,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 3.9
      }
    ]
  },
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "172ba7d46c202e679f3ccb10264c67416aaeb1c4",
              "lessThan": "b5dbecc2016e1692fd1c2532af9c41ba729cb747",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "0b5b831122fc3789fff75be433ba3e4dd7b779d4",
              "lessThan": "23e97d594ddd0153020c506d5041048fbde1beb4",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "73f7da5fd124f2cda9161e2e46114915e6e82e97",
              "lessThan": "737873a59905a54ca0d2d127ef882f3f88bf4379",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "3f14b377d01d8357eba032b4cabc8c1149b458b6",
              "lessThan": "47d99828591d0fe8be4b9c8992ff3b8e47968db9",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "3f14b377d01d8357eba032b4cabc8c1149b458b6",
              "lessThan": "b47bb899e04b5407c5a63fe88d4b6676586a6e84",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "3f14b377d01d8357eba032b4cabc8c1149b458b6",
              "lessThan": "439d3e404f9d5e515911cc8132cde198b337c19e",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "3f14b377d01d8357eba032b4cabc8c1149b458b6",
              "lessThan": "8a7ed561671aa6a911a2de99e59ef670a4d0b1df",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "f5346df0591d10bc948761ca854b1fae6d2ef441",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5.15.148",
              "lessThan": "5.15.217",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "6.1.75",
              "lessThan": "6.1.184",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "6.6.14",
              "lessThan": "6.6.152",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "6.7.2",
              "lessThan": "6.8",
              "versionType": "semver"
            }
          ],
          "programFiles": [
            "net/sched/act_ct.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.8"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "6.8",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "5.15.217",
              "versionType": "semver",
              "lessThanOrEqual": "5.15.*"
            },
            {
              "status": "unaffected",
              "version": "6.1.184",
              "versionType": "semver",
              "lessThanOrEqual": "6.1.*"
            },
            {
              "status": "unaffected",
              "version": "6.6.152",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
              "status": "unaffected",
              "version": "6.12.104",
              "versionType": "semver",
              "lessThanOrEqual": "6.12.*"
            },
            {
              "status": "unaffected",
              "version": "6.18.45",
              "versionType": "semver",
              "lessThanOrEqual": "6.18.*"
            },
            {
              "status": "unaffected",
              "version": "7.1.9",
              "versionType": "semver",
              "lessThanOrEqual": "7.1.*"
            },
            {
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "net/sched/act_ct.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-08-22T16:16:34.897",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/23e97d594ddd0153020c506d5041048fbde1beb4",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/439d3e404f9d5e515911cc8132cde198b337c19e",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/47d99828591d0fe8be4b9c8992ff3b8e47968db9",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/737873a59905a54ca0d2d127ef882f3f88bf4379",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/8a7ed561671aa6a911a2de99e59ef670a4d0b1df",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/b47bb899e04b5407c5a63fe88d4b6676586a6e84",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/b5dbecc2016e1692fd1c2532af9c41ba729cb747",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: act_ct: fix sk_buff leak when the header checks reject a packet\n\ntcf_ct_handle_fragments() runs its header sanity checks before handing\nanything to the defragmentation engine:\n\n\tif (family == NFPROTO_IPV4)\n\t\terr = tcf_ct_ipv4_is_fragment(skb, &frag);\n\telse\n\t\terr = tcf_ct_ipv6_is_fragment(skb, &frag);\n\tif (err || !frag)\n\t\treturn err;\n\ntcf_ct_ipv4_is_fragment() returns -EINVAL or -ENOMEM;\ntcf_ct_ipv6_is_fragment() adds -EPROTO when ipv6_find_hdr() fails. None of\nthem frees or queues the skb, so on that path the caller still owns it.\n\ntcf_ct_act() however funnels every non-zero return into the\nownership-transfer exit:\n\n\terr = tcf_ct_handle_fragments(net, skb, family, p->zone, &defrag);\n\tif (err)\n\t\tgoto out_frag;\n\t...\nout_frag:\n\tif (err != -EINPROGRESS)\n\t\ttcf_action_inc_drop_qstats(&c->common);\n\treturn TC_ACT_CONSUMED;\n\nTC_ACT_CONSUMED means the action took ownership of the skb, so no caller\nfrees it - sch_handle_ingress(), sch_handle_egress() and\ntcf_qevent_handle() all deliberately skip the free for that verdict. The\nskb is therefore orphaned: one sk_buff plus its data buffer is leaked per\nmalformed packet, unbounded. Note the drop counter is already incremented\nfor these errors, so the statistics claim a drop that never happens.\n\nThree different ownership states reach out_frag: today - the skb may be\nqueued by the defrag engine (-EINPROGRESS), already freed by\nnf_ct_handle_fragments(), or still owned by us. Tell the caller which of\nthose it is, and free the packet ourselves in the last case, which\nrestores the TC_ACT_SHOT behaviour that predated the Fixes: commit.\n\nReproduced on v7.2-rc6 with a 54-byte frame carrying a 40-byte IPv6\nheader with nexthdr = 0 (hop-by-hop) and nothing after it, on a\nclsact ingress chain with \"action ct\". kmemleak reports one leaked\n232-byte skbuff_head_cache object plus its 704-byte data buffer per\npacket; with this patch it reports none."
    }
  ],
  "lastModified": "2026-08-25T06:18:40.510",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}