CVE-2026-90076 (GCVE-0-2026-90076)

Vulnerability from cvelistv5 – Published: 2026-09-17 16:05 – Updated: 2026-09-17 16:05
VLAI
Title
net/sched: fq: add overflow bounds to quantum and initial quantum
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: fq: add overflow bounds to quantum and initial quantum fq_init() computes quantum = 2 * psched_mtu() and initial_quantum = 10 * psched_mtu() with no overflow check. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000; the 2 * and 10 * multiplications wrap to 0 in 32-bit arithmetic, so q->quantum == 0. Then in fq_dequeue() the credit-refill loop adds 0 to f->credit (which stays <= 0) and goto begin loops forever under the qdisc lock, creating a soft lockup. Clamp psched_mtu() to [1, 1 << 20] before multiplying so the product cannot wrap, then cap the result at 1 << 20, matching the bound already enforced on TCA_FQ_QUANTUM in fq_change(). Conditions to recreate the bug: a device whose MTU (plus hard_header_len) is large enough that 2 * psched_mtu() wraps (e.g. a dummy device with max_mtu == 0 accepting MTU 2147483634). Requires CAP_NET_ADMIN in a user namespace.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: afe4fd062416b158a8a8538b23adc1930a9b88dc , < d16dac3925be95ad46e986d4b139c9898b6e227f (git)
Affected: afe4fd062416b158a8a8538b23adc1930a9b88dc , < f6b3e3848a5fca63438984acd6d9eceac80814c1 (git)
Affected: afe4fd062416b158a8a8538b23adc1930a9b88dc , < e35acd56f244d94355f9ab237c2ecc8fba5e6f04 (git)
Affected: afe4fd062416b158a8a8538b23adc1930a9b88dc , < 709f34f7c28dc4dd6c40343d101850f11e172312 (git)
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Linux Linux Affected: 3.12
Unaffected: 0 , < 3.12 (semver)
Unaffected: 6.12.110 , ≤ 6.12.* (semver)
Unaffected: 6.18.52 , ≤ 6.18.* (semver)
Unaffected: 7.2.6 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sched/sch_fq.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "afe4fd062416b158a8a8538b23adc1930a9b88dc",
              "versionType": "git"
            },
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              "versionType": "git"
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              "versionType": "git"
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          "product": "Linux",
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          "vendor": "Linux",
          "versions": [
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              "version": "3.12"
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              "status": "unaffected",
              "version": "0",
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              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.18.52",
              "versionType": "semver"
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              "versionType": "semver"
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              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
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        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.110",
                  "versionStartIncluding": "3.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.6",
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                  "vulnerable": true
                },
                {
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                  "versionEndExcluding": "7.3-rc1",
                  "versionStartIncluding": "3.12",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq: add overflow bounds to quantum and initial quantum\n\nfq_init() computes quantum = 2 * psched_mtu() and initial_quantum = 10 *\npsched_mtu() with no overflow check. A device with a huge MTU (e.g. dummy\nwith max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return\n0x80000000; the 2 * and 10 * multiplications wrap to 0 in 32-bit\narithmetic, so q-\u003equantum == 0. Then in fq_dequeue() the credit-refill\nloop adds 0 to f-\u003ecredit (which stays \u003c= 0) and goto begin loops\nforever under the qdisc lock, creating a soft lockup.\n\nClamp psched_mtu() to [1, 1 \u003c\u003c 20] before multiplying so the product\ncannot wrap, then cap the result at 1 \u003c\u003c 20, matching the bound already\nenforced on TCA_FQ_QUANTUM in fq_change().\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) is large enough that 2 * psched_mtu() wraps (e.g. a\ndummy device with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-17T16:05:55.517Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/d16dac3925be95ad46e986d4b139c9898b6e227f"
        },
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          "url": "https://git.kernel.org/stable/c/f6b3e3848a5fca63438984acd6d9eceac80814c1"
        },
        {
          "url": "https://git.kernel.org/stable/c/e35acd56f244d94355f9ab237c2ecc8fba5e6f04"
        },
        {
          "url": "https://git.kernel.org/stable/c/709f34f7c28dc4dd6c40343d101850f11e172312"
        }
      ],
      "title": "net/sched: fq: add overflow bounds to quantum and initial quantum",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90076",
    "datePublished": "2026-09-17T16:05:55.517Z",
    "dateReserved": "2026-09-11T19:38:34.785Z",
    "dateUpdated": "2026-09-17T16:05:55.517Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
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      "date": "2026-09-25",
      "epss": "0.00209",
      "percentile": "0.09867"
    },
    "nvd": {
      "cve": {
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            "affectedData": [
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                "defaultStatus": "unaffected",
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                "programFiles": [
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                ],
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              },
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                    "versionType": "semver"
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                    "version": "6.18.52",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "7.2.*",
                    "status": "unaffected",
                    "version": "7.2.6",
                    "versionType": "semver"
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                  }
                ]
              }
            ],
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq: add overflow bounds to quantum and initial quantum\n\nfq_init() computes quantum = 2 * psched_mtu() and initial_quantum = 10 *\npsched_mtu() with no overflow check. A device with a huge MTU (e.g. dummy\nwith max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return\n0x80000000; the 2 * and 10 * multiplications wrap to 0 in 32-bit\narithmetic, so q-\u003equantum == 0. Then in fq_dequeue() the credit-refill\nloop adds 0 to f-\u003ecredit (which stays \u003c= 0) and goto begin loops\nforever under the qdisc lock, creating a soft lockup.\n\nClamp psched_mtu() to [1, 1 \u003c\u003c 20] before multiplying so the product\ncannot wrap, then cap the result at 1 \u003c\u003c 20, matching the bound already\nenforced on TCA_FQ_QUANTUM in fq_change().\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) is large enough that 2 * psched_mtu() wraps (e.g. a\ndummy device with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace."
          }
        ],
        "id": "CVE-2026-90076",
        "lastModified": "2026-09-17T17:16:56.820",
        "metrics": {},
        "published": "2026-09-17T17:16:56.820",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    }
  }
}



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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.

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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.
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  • 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.



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.