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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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sched/cls_u32.c"
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "lessThan": "313cb9ffc4101a885d791facf4b5ea3d5e06144d",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "aef96eead2860cbfa371e4471d4f04412213b958",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            }
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          "product": "Linux",
          "programFiles": [
            "net/sched/cls_u32.c"
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.12"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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      "cpeApplicability": [
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          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "versionStartIncluding": "2.6.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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              "operator": "OR"
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      "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()."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "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": [
            {
              "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."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:48:31.015Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/313cb9ffc4101a885d791facf4b5ea3d5e06144d"
        },
        {
          "url": "https://git.kernel.org/stable/c/aef96eead2860cbfa371e4471d4f04412213b958"
        }
      ],
      "title": "net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds",
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        "engine": "bippy-1.2.0"
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "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"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "date": "2026-09-20",
      "epss": "0.00121",
      "percentile": "0.02198"
    },
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      "current_release_date": "2026-08-23T14:58:12.000Z",
      "cve": "CVE-2026-74544",
      "id": "msrc_CVE-2026-74544",
      "initial_release_date": "2026-08-23T14:58:12.000Z",
      "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": {
        "affected": [
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                "product": "Linux",
                "programFiles": [
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                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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                    "versionType": "git"
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                "vendor": "Linux",
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                  },
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                    "status": "unaffected",
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                  }
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        "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()."
          }
        ],
        "id": "CVE-2026-74544",
        "lastModified": "2026-08-17T06:19:51.597",
        "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"
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              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
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        "published": "2026-08-15T13:17:59.753",
        "references": [
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/313cb9ffc4101a885d791facf4b5ea3d5e06144d"
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            "url": "https://git.kernel.org/stable/c/aef96eead2860cbfa371e4471d4f04412213b958"
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        "vulnStatus": "Received"
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      "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"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-02T01:04:26Z",
      "cve": "CVE-2026-74544",
      "id": "CVE-2026-74544",
      "initial_release_date": "2026-08-15T23:50:37Z",
      "product_status:known_not_affected": "362",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-74544",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-74544.json",
      "version": "3"
    }
  }
}



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  • 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.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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