FKIE_CVE-2025-39677

Vulnerability from fkie_nvd - Published: 2025-09-05 18:15 - Updated: 2026-10-30 13:18
Severity
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
5.5 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: Fix backlog accounting in qdisc_dequeue_internal This issue applies for the following qdiscs: hhf, fq, fq_codel, and fq_pie, and occurs in their change handlers when adjusting to the new limit. The problem is the following in the values passed to the subsequent qdisc_tree_reduce_backlog call given a tbf parent: When the tbf parent runs out of tokens, skbs of these qdiscs will be placed in gso_skb. Their peek handlers are qdisc_peek_dequeued, which accounts for both qlen and backlog. However, in the case of qdisc_dequeue_internal, ONLY qlen is accounted for when pulling from gso_skb. This means that these qdiscs are missing a qdisc_qstats_backlog_dec when dropping packets to satisfy the new limit in their change handlers. One can observe this issue with the following (with tc patched to support a limit of 0): export TARGET=fq tc qdisc del dev lo root tc qdisc add dev lo root handle 1: tbf rate 8bit burst 100b latency 1ms tc qdisc replace dev lo handle 3: parent 1:1 $TARGET limit 1000 echo ''; echo 'add child'; tc -s -d qdisc show dev lo ping -I lo -f -c2 -s32 -W0.001 127.0.0.1 2>&1 >/dev/null echo ''; echo 'after ping'; tc -s -d qdisc show dev lo tc qdisc change dev lo handle 3: parent 1:1 $TARGET limit 0 echo ''; echo 'after limit drop'; tc -s -d qdisc show dev lo tc qdisc replace dev lo handle 2: parent 1:1 sfq echo ''; echo 'post graft'; tc -s -d qdisc show dev lo The second to last show command shows 0 packets but a positive number (74) of backlog bytes. The problem becomes clearer in the last show command, where qdisc_purge_queue triggers qdisc_tree_reduce_backlog with the positive backlog and causes an underflow in the tbf parent's backlog (4096 Mb instead of 0). To fix this issue, the codepath for all clients of qdisc_dequeue_internal has been simplified: codel, pie, hhf, fq, fq_pie, and fq_codel. qdisc_dequeue_internal handles the backlog adjustments for all cases that do not directly use the dequeue handler. The old fq_codel_change limit adjustment loop accumulated the arguments to the subsequent qdisc_tree_reduce_backlog call through the cstats field. However, this is confusing and error prone as fq_codel_dequeue could also potentially mutate this field (which qdisc_dequeue_internal calls in the non gso_skb case), so we have unified the code here with other qdiscs.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/38cdf8d1f5f3ee133f6e48dd422df4057fa9bfcb
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/52bf272636bda69587952b35ae97690b8dc89941Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/65d1b5d84a0d697e9cfcdd0e07aad1bf1cb96295
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a225f44d84b8900d679c5f5a9ea46fe9c0cc7802Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/dcfed7251e23cd71d32c4ecc444ff97992087e46
Impacted products
Vendor Product Version
linux linux_kernel *
linux linux_kernel 6.17
linux linux_kernel 6.17
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/net/sch_generic.h",
            "net/sched/sch_codel.c",
            "net/sched/sch_fq.c",
            "net/sched/sch_fq_codel.c",
            "net/sched/sch_fq_pie.c",
            "net/sched/sch_hhf.c",
            "net/sched/sch_pie.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "65d1b5d84a0d697e9cfcdd0e07aad1bf1cb96295",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "dcfed7251e23cd71d32c4ecc444ff97992087e46",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "38cdf8d1f5f3ee133f6e48dd422df4057fa9bfcb",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "a225f44d84b8900d679c5f5a9ea46fe9c0cc7802",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            },
            {
              "lessThan": "52bf272636bda69587952b35ae97690b8dc89941",
              "status": "affected",
              "version": "4b549a2ef4bef9965d97cbd992ba67930cd3e0fe",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "include/net/sch_generic.h",
            "net/sched/sch_codel.c",
            "net/sched/sch_fq.c",
            "net/sched/sch_fq_codel.c",
            "net/sched/sch_fq_pie.c",
            "net/sched/sch_hhf.c",
            "net/sched/sch_pie.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "3.5"
            },
            {
              "lessThan": "3.5",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.191",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.160",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.114",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.16.*",
              "status": "unaffected",
              "version": "6.16.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.17",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "6C2046DB-71F9-451C-B88C-B00FB2E419A2",
              "versionEndExcluding": "6.16.4",
              "versionStartIncluding": "3.5",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:6.17:rc1:*:*:*:*:*:*",
              "matchCriteriaId": "327D22EF-390B-454C-BD31-2ED23C998A1C",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:o:linux:linux_kernel:6.17:rc2:*:*:*:*:*:*",
              "matchCriteriaId": "C730CD9A-D969-4A8E-9522-162AAF7C0EE9",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Fix backlog accounting in qdisc_dequeue_internal\n\nThis issue applies for the following qdiscs: hhf, fq, fq_codel, and\nfq_pie, and occurs in their change handlers when adjusting to the new\nlimit. The problem is the following in the values passed to the\nsubsequent qdisc_tree_reduce_backlog call given a tbf parent:\n\n   When the tbf parent runs out of tokens, skbs of these qdiscs will\n   be placed in gso_skb. Their peek handlers are qdisc_peek_dequeued,\n   which accounts for both qlen and backlog. However, in the case of\n   qdisc_dequeue_internal, ONLY qlen is accounted for when pulling\n   from gso_skb. This means that these qdiscs are missing a\n   qdisc_qstats_backlog_dec when dropping packets to satisfy the\n   new limit in their change handlers.\n\n   One can observe this issue with the following (with tc patched to\n   support a limit of 0):\n\n   export TARGET=fq\n   tc qdisc del dev lo root\n   tc qdisc add dev lo root handle 1: tbf rate 8bit burst 100b latency 1ms\n   tc qdisc replace dev lo handle 3: parent 1:1 $TARGET limit 1000\n   echo \u0027\u0027; echo \u0027add child\u0027; tc -s -d qdisc show dev lo\n   ping -I lo -f -c2 -s32 -W0.001 127.0.0.1 2\u003e\u00261 \u003e/dev/null\n   echo \u0027\u0027; echo \u0027after ping\u0027; tc -s -d qdisc show dev lo\n   tc qdisc change dev lo handle 3: parent 1:1 $TARGET limit 0\n   echo \u0027\u0027; echo \u0027after limit drop\u0027; tc -s -d qdisc show dev lo\n   tc qdisc replace dev lo handle 2: parent 1:1 sfq\n   echo \u0027\u0027; echo \u0027post graft\u0027; tc -s -d qdisc show dev lo\n\n   The second to last show command shows 0 packets but a positive\n   number (74) of backlog bytes. The problem becomes clearer in the\n   last show command, where qdisc_purge_queue triggers\n   qdisc_tree_reduce_backlog with the positive backlog and causes an\n   underflow in the tbf parent\u0027s backlog (4096 Mb instead of 0).\n\nTo fix this issue, the codepath for all clients of qdisc_dequeue_internal\nhas been simplified: codel, pie, hhf, fq, fq_pie, and fq_codel.\nqdisc_dequeue_internal handles the backlog adjustments for all cases that\ndo not directly use the dequeue handler.\n\nThe old fq_codel_change limit adjustment loop accumulated the arguments to\nthe subsequent qdisc_tree_reduce_backlog call through the cstats field.\nHowever, this is confusing and error prone as fq_codel_dequeue could also\npotentially mutate this field (which qdisc_dequeue_internal calls in the\nnon gso_skb case), so we have unified the code here with other qdiscs."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nnet/sched: Correcci\u00f3n de la contabilidad del backlog en qdisc_dequeue_internal\n\nEste problema se aplica a los siguientes qdiscs: hhf, fq, fq_codel, y fq_pie, y ocurre en sus gestores de cambio al ajustarse al nuevo l\u00edmite. El problema es el siguiente en los valores pasados a la subsiguiente llamada a qdisc_tree_reduce_backlog dado un padre tbf:\n\n   Cuando el padre tbf se queda sin tokens, los skbs de estos qdiscs se colocar\u00e1n en gso_skb. Sus gestores de peek son qdisc_peek_dequeued, que contabiliza tanto qlen como backlog. Sin embargo, en el caso de qdisc_dequeue_internal, S\u00d3LO qlen se contabiliza al extraer de gso_skb. Esto significa que a estos qdiscs les falta un qdisc_qstats_backlog_dec al descartar paquetes para satisfacer el nuevo l\u00edmite en sus gestores de cambio.\n\n   Se puede observar este problema con lo siguiente (con tc parcheado para soportar un l\u00edmite de 0):\n\n   export TARGET=fq\n   tc qdisc del dev lo root\n   tc qdisc add dev lo root handle 1: tbf rate 8bit burst 100b latency 1ms\n   tc qdisc replace dev lo handle 3: parent 1:1 $TARGET limit 1000\n   echo \u0027\u0027; echo \u0027add child\u0027; tc -s -d qdisc show dev lo\n   ping -I lo -f -c2 -s32 -W0.001 127.0.0.1 2\u003e\u00261 \u003e/dev/null\n   echo \u0027\u0027; echo \u0027after ping\u0027; tc -s -d qdisc show dev lo\n   tc qdisc change dev lo handle 3: parent 1:1 $TARGET limit 0\n   echo \u0027\u0027; echo \u0027after limit drop\u0027; tc -s -d qdisc show dev lo\n   tc qdisc replace dev lo handle 2: parent 1:1 sfq\n   echo \u0027\u0027; echo \u0027post graft\u0027; tc -s -d qdisc show dev lo\n\n   El pen\u00faltimo comando show muestra 0 paquetes pero un n\u00famero positivo (74) de bytes de backlog. El problema se vuelve m\u00e1s claro en el \u00faltimo comando show, donde qdisc_purge_queue activa qdisc_tree_reduce_backlog con el backlog positivo y causa un desbordamiento negativo en el backlog del padre tbf (4096 Mb en lugar de 0).\n\nPara solucionar este problema, la ruta de c\u00f3digo para todos los clientes de qdisc_dequeue_internal ha sido simplificada: codel, pie, hhf, fq, fq_pie, y fq_codel. qdisc_dequeue_internal gestiona los ajustes del backlog para todos los casos que no utilizan directamente el gestor de dequeue.\n\nEl antiguo bucle de ajuste de l\u00edmite fq_codel_change acumulaba los argumentos para la subsiguiente llamada a qdisc_tree_reduce_backlog a trav\u00e9s del campo cstats. Sin embargo, esto es confuso y propenso a errores ya que fq_codel_dequeue tambi\u00e9n podr\u00eda mutar este campo (que qdisc_dequeue_internal llama en el caso no gso_skb), por lo que hemos unificado el c\u00f3digo aqu\u00ed con otros qdiscs."
    }
  ],
  "id": "CVE-2025-39677",
  "lastModified": "2026-10-30T13:18:08.420",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 5.9,
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "type": "Secondary"
      },
      {
        "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"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2025-39677",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-10-15T21:53:13.090718Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2025-09-05T18:15:44.043",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/38cdf8d1f5f3ee133f6e48dd422df4057fa9bfcb"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/52bf272636bda69587952b35ae97690b8dc89941"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/65d1b5d84a0d697e9cfcdd0e07aad1bf1cb96295"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "tags": [
        "Patch"
      ],
      "url": "https://git.kernel.org/stable/c/a225f44d84b8900d679c5f5a9ea46fe9c0cc7802"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/dcfed7251e23cd71d32c4ecc444ff97992087e46"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "NVD-CWE-noinfo"
        }
      ],
      "source": "nvd@nist.gov",
      "type": "Primary"
    }
  ]
}



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