CVE-2026-98427 (GCVE-0-2026-98427)

Vulnerability from cvelistv5 – Published: 2026-10-14 13:27 – Updated: 2026-10-14 13:27
VLAI
Title
net/sched: codel: bound the dropping loop per dequeue call
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: codel: bound the dropping loop per dequeue call The CoDel control law schedules the next drop one interval/sqrt(count) after the previous drop, using the configured interval (codel_params.interval). For very small intervals the scheduled step rounds down to zero, so the dropping loop in codel_dequeue() never advances and drains the entire backlog under the qdisc lock in one call - an unprivileged user can trigger a soft lockup this way. Fix in the shared codel code used by both codel and fq_codel: 1. Make the control-law step at least 1 tick so the dropping loop always moves forward. 2. Cap the dropping loop at CODEL_MAX_DROPS_PER_DEQUEUE (256) drops per codel_dequeue() call, resyncing drop_next to now when the cap is hit: the catch-up owed to the loop grows with the idle gap and the backlog, which no interval threshold can bound. This is a deliberate behaviour change after long idle gaps. The cap applies to fq_codel (4b549a2ef4be) and the mac80211 TXQ path (fixed interval, cap only). The target sojourn delay (codel_params.target) is not validated: it does not feed the control law, so a sub-tick value is aggressive rather than deadlock-prone. Conditions to recreate the bug: - tc qdisc add dev lo root handle 1: tbf rate 1kbit burst 2kb limit 1000000 - tc qdisc add dev lo parent 1:1 handle 10: codel interval 2us target 1ms noecn limit 1000000 (same for fq_codel) - unpatched kernel: tc accepts it; a UDP flood under the 1kbit tbf soft-lockups (watchdog: BUG: soft lockup) while one codel_dequeue() call drops the backlog under the qdisc lock - patched kernel: same setup, at most 256 drops per dequeue call, no soft lockup Testing: claim reproducer and interval 2us/3us variants run clean; tdc qdisc category passes (see the selftests patch).
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6666 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 76e3cc126bb223013a6b9a0e2a51238d1ef2e409 , < bacd72289d34d8c05b7de5a12448b87b6dd93878 (git)
Affected: 76e3cc126bb223013a6b9a0e2a51238d1ef2e409 , < 7f4a5ec6258fd7c92633ec4b0493fc51166d9398 (git)
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Linux Linux Affected: 3.5
Unaffected: 0 , < 3.5 (semver)
Unaffected: 7.2.8 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc4 , ≤ * (original_commit_for_fix)
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Show details on NVD website
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/net/codel.h",
            "include/net/codel_impl.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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            }
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      ],
      "cpeApplicability": [
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          "nodes": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "vulnerable": true
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                  "versionStartIncluding": "3.5",
                  "vulnerable": true
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: codel: bound the dropping loop per dequeue call\n\nThe CoDel control law schedules the next drop one interval/sqrt(count)\nafter the previous drop, using the configured interval\n(codel_params.interval). For very small intervals the scheduled step\nrounds down to zero, so the dropping loop in codel_dequeue() never\nadvances and drains the entire backlog under the qdisc lock in one\ncall - an unprivileged user can trigger a soft lockup this way.\n\nFix in the shared codel code used by both codel and fq_codel:\n\n1. Make the control-law step at least 1 tick so the dropping loop\n   always moves forward.\n\n2. Cap the dropping loop at CODEL_MAX_DROPS_PER_DEQUEUE (256) drops\n   per codel_dequeue() call, resyncing drop_next to now when the cap\n   is hit: the catch-up owed to the loop grows with the idle gap and\n   the backlog, which no interval threshold can bound. This is a\n   deliberate behaviour change after long idle gaps.\n\nThe cap applies to fq_codel (4b549a2ef4be) and the mac80211 TXQ path\n(fixed interval, cap only).\n\nThe target sojourn delay (codel_params.target) is not validated: it\ndoes not feed the control law, so a sub-tick value is aggressive\nrather than deadlock-prone.\n\nConditions to recreate the bug:\n  - tc qdisc add dev lo root handle 1: tbf rate 1kbit burst 2kb limit 1000000\n  - tc qdisc add dev lo parent 1:1 handle 10: codel interval 2us target 1ms noecn limit 1000000 (same for fq_codel)\n  - unpatched kernel: tc accepts it; a UDP flood under the 1kbit tbf\n    soft-lockups (watchdog: BUG: soft lockup) while one\n    codel_dequeue() call drops the backlog under the qdisc lock\n  - patched kernel: same setup, at most 256 drops per dequeue call,\n    no soft lockup\n\nTesting: claim reproducer and interval 2us/3us variants run clean;\ntdc qdisc category passes (see the selftests patch)."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-14T13:27:53.770Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/bacd72289d34d8c05b7de5a12448b87b6dd93878"
        },
        {
          "url": "https://git.kernel.org/stable/c/7f4a5ec6258fd7c92633ec4b0493fc51166d9398"
        }
      ],
      "title": "net/sched: codel: bound the dropping loop per dequeue call",
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98427",
    "datePublished": "2026-10-14T13:27:53.770Z",
    "dateReserved": "2026-09-25T10:25:14.348Z",
    "dateUpdated": "2026-10-14T13:27:53.770Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "date": "2026-10-16",
      "epss": "0.00198",
      "percentile": "0.08941"
    },
    "microsoft_vex": {
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      "cve": "CVE-2026-98427",
      "id": "msrc_CVE-2026-98427",
      "initial_release_date": "2026-10-16T01:03:38.000Z",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "net/sched: codel: bound the dropping loop per dequeue call",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-98427.json",
      "version": "1"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
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              {
                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
                  "include/net/codel.h",
                  "include/net/codel_impl.h"
                ],
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                    "versionType": "semver"
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: codel: bound the dropping loop per dequeue call\n\nThe CoDel control law schedules the next drop one interval/sqrt(count)\nafter the previous drop, using the configured interval\n(codel_params.interval). For very small intervals the scheduled step\nrounds down to zero, so the dropping loop in codel_dequeue() never\nadvances and drains the entire backlog under the qdisc lock in one\ncall - an unprivileged user can trigger a soft lockup this way.\n\nFix in the shared codel code used by both codel and fq_codel:\n\n1. Make the control-law step at least 1 tick so the dropping loop\n   always moves forward.\n\n2. Cap the dropping loop at CODEL_MAX_DROPS_PER_DEQUEUE (256) drops\n   per codel_dequeue() call, resyncing drop_next to now when the cap\n   is hit: the catch-up owed to the loop grows with the idle gap and\n   the backlog, which no interval threshold can bound. This is a\n   deliberate behaviour change after long idle gaps.\n\nThe cap applies to fq_codel (4b549a2ef4be) and the mac80211 TXQ path\n(fixed interval, cap only).\n\nThe target sojourn delay (codel_params.target) is not validated: it\ndoes not feed the control law, so a sub-tick value is aggressive\nrather than deadlock-prone.\n\nConditions to recreate the bug:\n  - tc qdisc add dev lo root handle 1: tbf rate 1kbit burst 2kb limit 1000000\n  - tc qdisc add dev lo parent 1:1 handle 10: codel interval 2us target 1ms noecn limit 1000000 (same for fq_codel)\n  - unpatched kernel: tc accepts it; a UDP flood under the 1kbit tbf\n    soft-lockups (watchdog: BUG: soft lockup) while one\n    codel_dequeue() call drops the backlog under the qdisc lock\n  - patched kernel: same setup, at most 256 drops per dequeue call,\n    no soft lockup\n\nTesting: claim reproducer and interval 2us/3us variants run clean;\ntdc qdisc category passes (see the selftests patch)."
          }
        ],
        "id": "CVE-2026-98427",
        "lastModified": "2026-10-14T14:17:54.343",
        "metrics": {},
        "published": "2026-10-14T14:17:54.343",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        "vulnStatus": "Received"
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      "current_release_date": "2026-10-15T12:56:24+00:00",
      "cve": "CVE-2026-98427",
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      "product_status:known_affected": "77",
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      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: net/sched: codel: bound the dropping loop per dequeue call",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98427.json",
      "version": "3"
    }
  }
}



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