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CVE-2026-74544 (GCVE-0-2026-74544)

Vulnerability from cvelistv5 – Published: 2026-08-15 12:27 – Updated: 2026-08-17 05:48
VLAI
Title
net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds u32_change() copies the user-provided tc_u32_sel.offshift (unsigned char, 0-255) into the kernel knode object without bounds validation. When a packet later hits u32_classify() with TC_U32_VAROFFSET set, it evaluates `ntohs(offmask & *data) >> offshift` where the left operand is a 16-bit value promoted to a 32-bit int. Any offshift >= 32 is undefined behavior per C11 6.5.7p3, triggerable by an unprivileged user via user/network namespaces. UBSAN: shift-out-of-bounds in net/sched/cls_u32.c:236:43 shift exponent 32 is too large for 32-bit type int Fix this by rejecting offshift >= 16 during filter creation in u32_change().
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 313cb9ffc4101a885d791facf4b5ea3d5e06144d (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < aef96eead2860cbfa371e4471d4f04412213b958 (git)
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Linux Linux Affected: 2.6.12
Unaffected: 0 , < 2.6.12 (semver)
Unaffected: 7.1.8 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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Show details on NVD website
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{
  "containers": {
    "cna": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sched/cls_u32.c"
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          "versions": [
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              "versionType": "git"
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              "status": "affected",
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                  "vulnerable": true
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: cls_u32: validate offshift to prevent shift-out-of-bounds\n\nu32_change() copies the user-provided tc_u32_sel.offshift (unsigned char,\n0-255) into the kernel knode object without bounds validation. When a\npacket later hits u32_classify() with TC_U32_VAROFFSET set, it evaluates\n`ntohs(offmask \u0026 *data) \u003e\u003e offshift` where the left operand is a 16-bit\nvalue promoted to a 32-bit int. Any offshift \u003e= 32 is undefined behavior\nper C11 6.5.7p3, triggerable by an unprivileged user via user/network\nnamespaces.\n\nUBSAN: shift-out-of-bounds in net/sched/cls_u32.c:236:43\nshift exponent 32 is too large for 32-bit type int\n\nFix this by rejecting offshift \u003e= 16 during filter creation in\nu32_change()."
        }
      ],
      "metrics": [
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
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              "lang": "en",
              "value": "AV:L - The bug is configured through RTM_NEWTFILTER rtnetlink (tc filter add) in u32_change(); per kernel CNA guidance, tc/qdisc/netlink classifier setup is Local even though subsequent packets invoke u32_classify() on ingress/egress paths.\nAC:L - The attacker fully controls offshift (32-255), TC_U32_VAROFFSET selector flags, and matching packet bytes when installing the filter and sending traffic through the attached qdisc; no race or external victim state is required.\nPR:L - Creating u32 filters requires CAP_NET_ADMIN, which an unprivileged local user obtains in a user/network namespace via unshare -Urn; rtnetlink enforces netlink_net_capable() against that namespace\u0027s user_ns, not only init-root.\nUI:N - The attacker installs the malicious u32 filter and injects triggering packets themselves within their namespace; no separate victim action (opening files, mounting media, clicking links) is needed.\nS:U - Corrupted classifier offset arithmetic and any resulting kernel crash stay within the host kernel\u0027s security authority; this is standard local kernel compromise, not a VM escape, IOMMU bypass, or sandbox boundary crossing.\nC:H - Undefined-behavior right-shift (offshift\u003e=32) on packet-derived values corrupts variable offset math in u32_classify(), driving attacker-influenced skb_header_pointer reads at unintended offsets; per CNA guidance, exploitable kernel memory-unsafe operations warrant High confidentiality impact.\nI:H - Invalid shift results corrupt off2 and unsigned off accumulation in the classifier hot path, derailing cls_u32 control flow; C11 undefined behavior in kernel packet classification is exploitable for integrity compromise and potential code execution per CNA memory-corruption guidance.\nA:H - Hitting u32_classify() with offshift\u003e=32 provokes documented UBSAN shift-out-of-bounds at cls_u32.c:236; undefined shifts can also trigger kernel oops/panic during packet classification, satisfying CNA guidance that kernel crashes are High availability impact."
            }
          ]
        }
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      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:48:31.015Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/313cb9ffc4101a885d791facf4b5ea3d5e06144d"
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        {
          "url": "https://git.kernel.org/stable/c/aef96eead2860cbfa371e4471d4f04412213b958"
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74544",
    "datePublished": "2026-08-15T12:27:53.941Z",
    "dateReserved": "2026-08-15T05:44:03.914Z",
    "dateUpdated": "2026-08-17T05:48:31.015Z",
    "state": "PUBLISHED"
  },
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      "cve": "CVE-2026-74544",
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      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-74544.json",
      "version": "1"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-74544\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-08-15T13:17:59.753\",\"lastModified\":\"2026-08-17T06:19:51.597\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nnet/sched: cls_u32: validate offshift to prevent shift-out-of-bounds\\n\\nu32_change() copies the user-provided tc_u32_sel.offshift (unsigned char,\\n0-255) into the kernel knode object without bounds validation. When a\\npacket later hits u32_classify() with TC_U32_VAROFFSET set, it evaluates\\n`ntohs(offmask \u0026 *data) \u003e\u003e offshift` where the left operand is a 16-bit\\nvalue promoted to a 32-bit int. Any offshift \u003e= 32 is undefined behavior\\nper C11 6.5.7p3, triggerable by an unprivileged user via user/network\\nnamespaces.\\n\\nUBSAN: shift-out-of-bounds in net/sched/cls_u32.c:236:43\\nshift exponent 32 is too large for 32-bit type int\\n\\nFix this by rejecting offshift \u003e= 16 during filter creation in\\nu32_change().\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"net/sched/cls_u32.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"313cb9ffc4101a885d791facf4b5ea3d5e06144d\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"aef96eead2860cbfa371e4471d4f04412213b958\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"net/sched/cls_u32.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"2.6.12\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"2.6.12\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1.8\",\"lessThanOrEqual\":\"7.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":7.8,\"baseSeverity\":\"HIGH\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":5.9}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/313cb9ffc4101a885d791facf4b5ea3d5e06144d\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/aef96eead2860cbfa371e4471d4f04412213b958\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-21T08:21:02+00:00",
      "cve": "CVE-2026-74544",
      "id": "CVE-2026-74544",
      "initial_release_date": "2026-08-15T00:00:00+00:00",
      "product_status:known_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74544.json",
      "version": "3"
    }
  }
}



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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.

Sightings

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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.
  • 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.


Detection rules are retrieved from Rulezet.