net_sched: Prevent creation of classes with TC_H_ROOT
In the Linux kernel, the following vulnerability has been resolved: net_sched: Prevent creation of classes with TC_H_ROOT The function qdisc_tree_reduce_backlog() uses TC_H_ROOT as a termination condition when traversing up the qdisc tree to update parent backlog counters. However, if a class is created with classid TC_H_ROOT, the traversal terminates prematurely at this class instead of reaching the actual root qdisc, causing parent statistics to be incorrectly maintained. In case of DRR, this could lead to a crash as reported by Mingi Cho. Prevent the creation of any Qdisc class with classid TC_H_ROOT (0xFFFFFFFF) across all qdisc types, as suggested by Jamal.
- Products
- Kernel
- Affected versions
- Not specified
- Fixed versions
- 5.10.236, 5.15.180, 5.4.292, 6.1.132, 6.12.20, 6.13.8, 6.6.84
- CVEs
- CVE-2025-21971
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 2 Nov 2026, 18:30 UTC · Revision 1
Source evidence
net_sched: Prevent creation of classes with TC_H_ROOT
core-osv · Original sourcePublished 1 Apr 2025, 15:47 UTC
In the Linux kernel, the following vulnerability has been resolved: net_sched: Prevent creation of classes with TC_H_ROOT The function qdisc_tree_reduce_backlog() uses TC_H_ROOT as a termination condition when traversing up the qdisc tree to update parent backlog counters. However, if a class is created with classid TC_H_ROOT, the traversal terminates prematurely at this class instead of reaching the actual root qdisc, causing parent statistics to be incorrectly maintained. In case of DRR, this could lead to a crash as reported by Mingi Cho. Prevent the creation of any Qdisc class with classid TC_H_ROOT (0xFFFFFFFF) across all qdisc types, as suggested by Jamal.
osv:CVE-2025-21971
Kernel
Fixed versions: 5.4.292, 5.10.236, 5.15.180, 6.1.132, 6.6.84, 6.12.20, 6.13.8
Complete source record
{
"id": "8a37bfb92dd4b2d952788fdfc0284c0b256a9b1067875963df20654fc8b43418",
"url": "https://osv.dev/vulnerability/CVE-2025-21971",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "net_sched: Prevent creation of classes with TC_H_ROOT",
"summary": "In the Linux kernel, the following vulnerability has been resolved: net_sched: Prevent creation of classes with TC_H_ROOT The function qdisc_tree_reduce_backlog() uses TC_H_ROOT as a termination condition when traversing up the qdisc tree to update parent backlog counters. However, if a class is created with classid TC_H_ROOT, the traversal terminates prematurely at this class instead of reaching the actual root qdisc, causing parent statistics to be incorrectly maintained. In case of DRR, this could lead to a crash as reported by Mingi Cho. Prevent the creation of any Qdisc class with classid TC_H_ROOT (0xFFFFFFFF) across all qdisc types, as suggested by Jamal.",
"evidence": "osv:CVE-2025-21971",
"products": [
{
"name": {
"value": "Kernel",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "5.4.292",
"evidence": "/affected/1/ranges"
},
{
"value": "5.10.236",
"evidence": "/affected/1/ranges"
},
{
"value": "5.15.180",
"evidence": "/affected/1/ranges"
},
{
"value": "6.1.132",
"evidence": "/affected/1/ranges"
},
{
"value": "6.6.84",
"evidence": "/affected/1/ranges"
},
{
"value": "6.12.20",
"evidence": "/affected/1/ranges"
},
{
"value": "6.13.8",
"evidence": "/affected/1/ranges"
}
],
"affected_versions": []
}
],
"severity": "high",
"structured": {
"id": "CVE-2025-21971",
"aliases": [
"CVE-2025-21971"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"type": "GIT",
"events": [
{
"introduced": "066a3b5b2346febf9a655b444567b7138e3bb939"
},
{
"fixed": "e05d9938b1b0ac40b6054cc5fa0ccbd9afd5ed4c"
},
{
"fixed": "7a82fe67a9f4d7123d8e5ba8f0f0806c28695006"
},
{
"fixed": "003d92c91cdb5a64b25a9a74cb8543aac9a8bb48"
},
{
"fixed": "e5ee00607bbfc97ef1526ea95b6b2458ac9e7cb7"
},
{
"fixed": "78533c4a29ac3aeddce4b481770beaaa4f3bfb67"
},
{
"fixed": "5c3ca9cb48b51bd72bf76b8b05e24f3cd53db5e7"
},
{
"fixed": "94edfdfb9505ab608e86599d1d1e38c83816fc1c"
},
{
"fixed": "0c3057a5a04d07120b3d0ec9c79568fceb9c921e"
}
]
}
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21971.json"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "2.6.25"
},
{
"fixed": "5.4.292"
}
]
},
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "5.5.0"
},
{
"fixed": "5.10.236"
}
]
},
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "5.11.0"
},
{
"fixed": "5.15.180"
}
]
},
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "5.16.0"
},
{
"fixed": "6.1.132"
}
]
},
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "6.2.0"
},
{
"fixed": "6.6.84"
}
]
},
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "6.7.0"
},
{
"fixed": "6.12.20"
}
]
},
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "6.13.0"
},
{
"fixed": "6.13.8"
}
]
}
],
"package": {
"name": "Kernel",
"ecosystem": "Linux"
},
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21971.json"
}
}
],
"modified": "2026-10-28T02:30:22.429885508Z",
"provider": "osv",
"references": [
"https://git.kernel.org/stable/c/003d92c91cdb5a64b25a9a74cb8543aac9a8bb48",
"https://git.kernel.org/stable/c/0c3057a5a04d07120b3d0ec9c79568fceb9c921e",
"https://git.kernel.org/stable/c/5c3ca9cb48b51bd72bf76b8b05e24f3cd53db5e7",
"https://git.kernel.org/stable/c/78533c4a29ac3aeddce4b481770beaaa4f3bfb67",
"https://git.kernel.org/stable/c/7a82fe67a9f4d7123d8e5ba8f0f0806c28695006",
"https://git.kernel.org/stable/c/94edfdfb9505ab608e86599d1d1e38c83816fc1c",
"https://git.kernel.org/stable/c/e05d9938b1b0ac40b6054cc5fa0ccbd9afd5ed4c",
"https://git.kernel.org/stable/c/e5ee00607bbfc97ef1526ea95b6b2458ac9e7cb7",
"https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html",
"https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21971.json",
"https://nvd.nist.gov/vuln/detail/CVE-2025-21971",
"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
],
"provider_metadata": {
"cna_assigner": "Linux",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21971.json"
}
},
"related_cves": [
{
"value": "CVE-2025-21971",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 488487,
"published_at": "2025-04-01T15:47:04.448+00:00"
}