CVE-2026-74739 (GCVE-0-2026-74739)
Vulnerability from cvelistv5 – Published: 2026-08-26 14:36 – Updated: 2026-08-27 05:01
VLAI
EPSS
VEX
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)
Assigner
References
6 references
Impacted products
2 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) |
guessed | |
| 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) |
guessed |
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"programFiles": [
"net/sched/cls_u32.c"
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"versionType": "semver"
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{
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"status": "unaffected",
"version": "6.12.105",
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{
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"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"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.1.184",
"versionStartIncluding": "4.14",
"vulnerable": true
},
{
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{
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},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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},
{
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}
],
"negate": false,
"operator": "OR"
}
]
}
],
"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": [
{
"url": "https://git.kernel.org/stable/c/ec5f3005586a785689fd568361b0c5925cb1548b"
},
{
"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": {
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"cveMetadata": {
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"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",
"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-74739",
"date": "2026-10-09",
"epss": "0.00176",
"percentile": "0.06535"
},
"microsoft_vex": {
"current_release_date": "2026-09-23T02:54:32.000Z",
"cve": "CVE-2026-74739",
"id": "msrc_CVE-2026-74739",
"initial_release_date": "2026-08-27T01:05:18.000Z",
"product_status:known_affected": "2",
"source": "Microsoft CSAF VEX",
"status": "final",
"title": "net/sched: cls_u32: skip hash tables in u32_bind_class()",
"url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-74739.json",
"version": "2"
},
"nvd": {
"cve": {
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"product": "Linux",
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},
{
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"status": "unaffected",
"version": "0",
"versionType": "semver"
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{
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{
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{
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"versionType": "semver"
},
{
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}
]
}
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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: 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": "CVE-2026-74739",
"lastModified": "2026-08-27T06:17:23.220",
"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"
},
"exploitabilityScore": 1.8,
"impactScore": 5.9,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
}
]
},
"published": "2026-08-26T15:16:52.603",
"references": [
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"url": "https://git.kernel.org/stable/c/19d114b93c94bdef70496f26685c2a6b242f41b3"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/31f26a95eeee926946809ac456c61a3217936a62"
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},
{
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},
{
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}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Received"
}
},
"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"
},
"suse_vex": {
"aggregate_severity": "moderate",
"current_release_date": "2026-10-08T17:00:47Z",
"cve": "CVE-2026-74739",
"id": "CVE-2026-74739",
"initial_release_date": "2026-08-27T00:21:29Z",
"product_status:known_affected": "388",
"product_status:known_not_affected": "4",
"source": "SUSE CSAF VEX",
"status": "interim",
"title": "SUSE CVE CVE-2026-74739",
"url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-74739.json",
"version": "7"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
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
| 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.
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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.
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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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.
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