CVE-2026-74739 (GCVE-0-2026-74739)

Vulnerability from cvelistv5 – Published: 2026-08-26 14:36 – Updated: 2026-08-27 05:01
VLAI
Title
net/sched: cls_u32: skip hash tables in u32_bind_class()
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_u32: skip hash tables in u32_bind_class() u32_walk() enumerates both struct tc_u_hnode and struct tc_u_knode through the walker callback. u32_bind_class() unconditionally casts the passed fh to tc_u_knode and accesses &n->res, so when fh is actually a tc_u_hnode, which has no tcf_result member, this results in a slab-out-of-bounds read of res->classid in tc_cls_bind_class(). The issue can be reproduced with the following commands: tc qdisc add dev lo root handle 1: hfsc tc class add dev lo parent 1: classid 1:1 hfsc sc rate 1000kbit tc filter add dev lo parent 1:1 protocol ip prio 1 u32 match u32 0 0 flowid 1:1 tc class add dev lo parent 1: classid 1:2 hfsc sc rate 2000kbit Fix this by skipping hash tables via the TC_U32_KEY(handle) check.
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: 07d79fc7d94e3f884b8b1c95aa615b202bb5e4c1 , < ec5f3005586a785689fd568361b0c5925cb1548b (git)
Affected: 07d79fc7d94e3f884b8b1c95aa615b202bb5e4c1 , < 19d114b93c94bdef70496f26685c2a6b242f41b3 (git)
Affected: 07d79fc7d94e3f884b8b1c95aa615b202bb5e4c1 , < 594a064d603202b9ee21e07679d854e5c1750cc4 (git)
Affected: 07d79fc7d94e3f884b8b1c95aa615b202bb5e4c1 , < 31f26a95eeee926946809ac456c61a3217936a62 (git)
Affected: 07d79fc7d94e3f884b8b1c95aa615b202bb5e4c1 , < e71f8e9ed6f311410b14741f6012afe01869c0fa (git)
Affected: 07d79fc7d94e3f884b8b1c95aa615b202bb5e4c1 , < 6d3724e616faf952c3adcf8414fc21a828ef3709 (git)
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Linux Linux Affected: 4.14
Unaffected: 0 , < 4.14 (semver)
Unaffected: 6.1.184 , ≤ 6.1.* (semver)
Unaffected: 6.6.153 , ≤ 6.6.* (semver)
Unaffected: 6.12.105 , ≤ 6.12.* (semver)
Unaffected: 6.18.46 , ≤ 6.18.* (semver)
Unaffected: 7.1.10 , ≤ 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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          "vendor": "Linux",
          "versions": [
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              "version": "4.14"
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              "status": "unaffected",
              "version": "0",
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              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.6.153",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.12.105",
              "versionType": "semver"
            },
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              "status": "unaffected",
              "version": "6.18.46",
              "versionType": "semver"
            },
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              "status": "unaffected",
              "version": "7.1.10",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
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      "cpeApplicability": [
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                  "versionStartIncluding": "4.14",
                  "vulnerable": true
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                  "versionEndExcluding": "6.6.153",
                  "versionStartIncluding": "4.14",
                  "vulnerable": true
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                  "vulnerable": true
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: cls_u32: skip hash tables in u32_bind_class()\n\nu32_walk() enumerates both struct tc_u_hnode and struct tc_u_knode\nthrough the walker callback. u32_bind_class() unconditionally casts the\npassed fh to tc_u_knode and accesses \u0026n-\u003eres, so when fh is actually a\ntc_u_hnode, which has no tcf_result member, this results in a\nslab-out-of-bounds read of res-\u003eclassid in tc_cls_bind_class().\n\nThe issue can be reproduced with the following commands:\n\n    tc qdisc add dev lo root handle 1: hfsc\n    tc class add dev lo parent 1: classid 1:1 hfsc sc rate 1000kbit\n    tc filter add dev lo parent 1:1 protocol ip prio 1 u32 match u32 0 0 flowid 1:1\n    tc class add dev lo parent 1: classid 1:2 hfsc sc rate 2000kbit\n\nFix this by skipping hash tables via the TC_U32_KEY(handle) check."
        }
      ],
      "metrics": [
        {
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            "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"
          },
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              "value": "AV:L - The bug is reached only via RTM_NEWTCLASS rtnetlink (tc class add) in __tc_ctl_tclass(), which calls tc_bind_tclass() to walk u32 filters; per kernel CNA guidance, tc/qdisc/netlink classifier configuration is Local, not remotely reachable by packets.\nAC:L - The reproducer is deterministic: install a u32 filter with flowid, then add another tc class so reverse binding walks hash nodes; the attacker controls every netlink step and needs no race or uncontrollable victim state.\nPR:L - RTM_NEWTCLASS requires CAP_NET_ADMIN enforced by netlink_net_capable() in rtnetlink; this capability is obtainable by unprivileged users in a user+network namespace (unshare -Urn) or containers granted NET_ADMIN, not init-namespace root only.\nUI:N - Exploitation requires only the attacker\u0027s own tc/netlink operations (qdisc, filter, class add) inside a namespace they control; no separate victim action such as opening files or mounting media is needed.\nS:U - Impact is kernel slab memory read and possible adjacent-slab corruption during tc class binding within the same host kernel; this is standard local kernel compromise, not VM escape, IOMMU bypass, or another cross-authority boundary.\nC:H - u32_bind_class() casts tc_u_hnode to tc_u_knode and reads \u0026n-\u003eres.classid past the hnode allocation in tc_cls_bind_class(); per CNA guidance, slab out-of-bounds reads of kernel memory warrant High confidentiality impact.\nI:H - If the out-of-bounds classid read matches the newly created class, tc_cls_bind_class() calls __tcf_bind_filter(), which xchg-writes to \u0026r-\u003eclass at the bogus offset, enabling adjacent slab corruption and potential control-flow hijack per memory-corruption guidance.\nA:H - The slab out-of-bounds access is reported as a KASAN violation on trigger, and mistaken reverse binding can corrupt adjacent kernel objects leading to oops/panic during later tc operations; per CNA guidance, kernel crashes and memory corruption score Availability High."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-27T05:01:00.695Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/ec5f3005586a785689fd568361b0c5925cb1548b"
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        {
          "url": "https://git.kernel.org/stable/c/19d114b93c94bdef70496f26685c2a6b242f41b3"
        },
        {
          "url": "https://git.kernel.org/stable/c/594a064d603202b9ee21e07679d854e5c1750cc4"
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          "url": "https://git.kernel.org/stable/c/31f26a95eeee926946809ac456c61a3217936a62"
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          "url": "https://git.kernel.org/stable/c/e71f8e9ed6f311410b14741f6012afe01869c0fa"
        },
        {
          "url": "https://git.kernel.org/stable/c/6d3724e616faf952c3adcf8414fc21a828ef3709"
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      ],
      "title": "net/sched: cls_u32: skip hash tables in u32_bind_class()",
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74739",
    "datePublished": "2026-08-26T14:36:51.746Z",
    "dateReserved": "2026-08-15T05:44:03.930Z",
    "dateUpdated": "2026-08-27T05:01:00.695Z",
    "state": "PUBLISHED"
  },
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      "date": "2026-09-01",
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      "percentile": "0.03523"
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-27T06:33:16+00:00",
      "cve": "CVE-2026-74739",
      "id": "CVE-2026-74739",
      "initial_release_date": "2026-08-26T00:00:00+00:00",
      "product_status:known_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: net/sched: cls_u32: skip hash tables in u32_bind_class()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74739.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.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.