Vulnerability-Lookup

GHSA-PHCW-98Q8-79WF

Vulnerability from github – Published: 2026-08-27 06:31 – Updated: 2026-08-27 06:31

Details

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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-74739"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-26T15:16:52Z",
    "severity": "HIGH"
  },
  "details": "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.",
  "id": "GHSA-phcw-98q8-79wf",
  "modified": "2026-08-27T06:31:30Z",
  "published": "2026-08-27T06:31:30Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-74739"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/19d114b93c94bdef70496f26685c2a6b242f41b3"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/31f26a95eeee926946809ac456c61a3217936a62"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/594a064d603202b9ee21e07679d854e5c1750cc4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6d3724e616faf952c3adcf8414fc21a828ef3709"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e71f8e9ed6f311410b14741f6012afe01869c0fa"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ec5f3005586a785689fd568361b0c5925cb1548b"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

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

Vulnerability from cvelistv5 – Published: 2026-08-26 14:36 – Updated: 2026-08-27 05:01

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

Linux mitre root

References

6 references

URL	Tags
https://git.kernel.org/stable/c/ec5f3005586a78568…
https://git.kernel.org/stable/c/19d114b93c94bdef7…
https://git.kernel.org/stable/c/594a064d603202b9e…
https://git.kernel.org/stable/c/31f26a95eeee92694…
https://git.kernel.org/stable/c/e71f8e9ed6f311410…
https://git.kernel.org/stable/c/6d3724e616faf952c…

Impacted products

2 products

Vendor	Product	Version
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)
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"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "ec5f3005586a785689fd568361b0c5925cb1548b",
              "status": "affected",
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              "versionType": "git"
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            {
              "lessThan": "19d114b93c94bdef70496f26685c2a6b242f41b3",
              "status": "affected",
              "version": "07d79fc7d94e3f884b8b1c95aa615b202bb5e4c1",
              "versionType": "git"
            },
            {
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              "status": "affected",
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              "versionType": "git"
            },
            {
              "lessThan": "31f26a95eeee926946809ac456c61a3217936a62",
              "status": "affected",
              "version": "07d79fc7d94e3f884b8b1c95aa615b202bb5e4c1",
              "versionType": "git"
            },
            {
              "lessThan": "e71f8e9ed6f311410b14741f6012afe01869c0fa",
              "status": "affected",
              "version": "07d79fc7d94e3f884b8b1c95aa615b202bb5e4c1",
              "versionType": "git"
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            {
              "lessThan": "6d3724e616faf952c3adcf8414fc21a828ef3709",
              "status": "affected",
              "version": "07d79fc7d94e3f884b8b1c95aa615b202bb5e4c1",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/sched/cls_u32.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.14"
            },
            {
              "lessThan": "4.14",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.184",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.153",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.105",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.46",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.10",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.184",
                  "versionStartIncluding": "4.14",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.153",
                  "versionStartIncluding": "4.14",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                {
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                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                },
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                }
              ],
              "negate": false,
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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": [
        {
          "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 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"
      },
      "references": [
        {
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        },
        {
          "url": "https://git.kernel.org/stable/c/19d114b93c94bdef70496f26685c2a6b242f41b3"
        },
        {
          "url": "https://git.kernel.org/stable/c/594a064d603202b9ee21e07679d854e5c1750cc4"
        },
        {
          "url": "https://git.kernel.org/stable/c/31f26a95eeee926946809ac456c61a3217936a62"
        },
        {
          "url": "https://git.kernel.org/stable/c/e71f8e9ed6f311410b14741f6012afe01869c0fa"
        },
        {
          "url": "https://git.kernel.org/stable/c/6d3724e616faf952c3adcf8414fc21a828ef3709"
        }
      ],
      "title": "net/sched: cls_u32: skip hash tables in u32_bind_class()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "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"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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