{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2025-21971", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2024-12-29T08:45:45.797Z", "datePublished": "2025-04-01T15:47:04.448Z", "dateUpdated": "2026-08-05T11:55:46.501Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T11:55:46.501Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet_sched: Prevent creation of classes with TC_H_ROOT\n\nThe function qdisc_tree_reduce_backlog() uses TC_H_ROOT as a termination\ncondition when traversing up the qdisc tree to update parent backlog\ncounters. However, if a class is created with classid TC_H_ROOT, the\ntraversal terminates prematurely at this class instead of reaching the\nactual root qdisc, causing parent statistics to be incorrectly maintained.\nIn case of DRR, this could lead to a crash as reported by Mingi Cho.\n\nPrevent the creation of any Qdisc class with classid TC_H_ROOT\n(0xFFFFFFFF) across all qdisc types, as suggested by Jamal." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The vulnerability is reached through RTM_NEWTCLASS rtnetlink messages (tc class add) plus locally generated traffic on a local netdev, requiring local system access. Per kernel scoring guidance, tc/netlink qdisc bugs are Local.\nAC:L - Exploitation is a deterministic fixed sequence — create a drr/hfsc/qfq/ets qdisc with handle ffff:, add a class with classid ffff:ffff, direct a packet to it, drop the filter, then delete the class — with no race window or attacker-uncontrollable precondition. Heap grooming to occupy the freed drr_class slab is fully under attacker control.\nPR:L - tc class creation requires only CAP_NET_ADMIN in the network namespace's owning user namespace (netlink_net_capable in rtnetlink_rcv_msg), which any unprivileged user obtains via unshare -Urn, where they can also create a dummy/veth device and generate the traffic needed. No real root in the init namespace is needed.\nUI:N - The attacker performs every step themselves — netlink configuration and packet transmission — with no action required from any other user or administrator.\nS:U - The corruption stays within the kernel's own security authority; there is no crossing of a VM, IOMMU, or sandbox boundary.\nC:H - The stale active-list entry produces a use-after-free on a kzalloc'd drr_class object; the attacker can reclaim that slab and have the kernel read pointers and data out of attacker-adjacent memory, and the resulting primitives can be leveraged for arbitrary kernel memory disclosure.\nI:H - The UAF yields both an unlink write (list_del on freed cl->alist) and an indirect call through cl->qdisc->ops->peek read from reclaimed heap memory, giving arbitrary write and control-flow hijack potential, i.e. full kernel integrity loss.\nA:H - Even without full exploitation, the dangling list entry causes a use-after-free oops in softirq context on the next dequeue, and the broken accounting permanently stalls the qdisc (drr_dequeue always returns NULL), halting transmission on the device — a repeatable kernel crash/DoS." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/sched/sch_api.c" ], "versions": [ { "version": "066a3b5b2346febf9a655b444567b7138e3bb939", "lessThan": "e05d9938b1b0ac40b6054cc5fa0ccbd9afd5ed4c", "status": "affected", "versionType": "git" }, { "version": "066a3b5b2346febf9a655b444567b7138e3bb939", "lessThan": "7a82fe67a9f4d7123d8e5ba8f0f0806c28695006", "status": "affected", "versionType": "git" }, { "version": "066a3b5b2346febf9a655b444567b7138e3bb939", "lessThan": "003d92c91cdb5a64b25a9a74cb8543aac9a8bb48", "status": "affected", "versionType": "git" }, { "version": "066a3b5b2346febf9a655b444567b7138e3bb939", "lessThan": "e5ee00607bbfc97ef1526ea95b6b2458ac9e7cb7", "status": "affected", "versionType": "git" }, { "version": "066a3b5b2346febf9a655b444567b7138e3bb939", "lessThan": "78533c4a29ac3aeddce4b481770beaaa4f3bfb67", "status": "affected", "versionType": "git" }, { "version": "066a3b5b2346febf9a655b444567b7138e3bb939", "lessThan": "5c3ca9cb48b51bd72bf76b8b05e24f3cd53db5e7", "status": "affected", "versionType": "git" }, { "version": "066a3b5b2346febf9a655b444567b7138e3bb939", "lessThan": "94edfdfb9505ab608e86599d1d1e38c83816fc1c", "status": "affected", "versionType": "git" }, { "version": "066a3b5b2346febf9a655b444567b7138e3bb939", "lessThan": "0c3057a5a04d07120b3d0ec9c79568fceb9c921e", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/sched/sch_api.c" ], "versions": [ { "version": "2.6.25", "status": "affected" }, { "version": "0", "lessThan": "2.6.25", "status": "unaffected", "versionType": "semver" }, { "version": "5.4.292", "lessThanOrEqual": "5.4.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.236", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.180", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.132", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.84", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.20", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.13.8", "lessThanOrEqual": "6.13.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.14", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.25", "versionEndExcluding": "5.4.292" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.25", "versionEndExcluding": "5.10.236" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.25", "versionEndExcluding": "5.15.180" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.25", "versionEndExcluding": "6.1.132" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.25", "versionEndExcluding": "6.6.84" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.25", "versionEndExcluding": "6.12.20" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.25", "versionEndExcluding": "6.13.8" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.25", "versionEndExcluding": "6.14" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/e05d9938b1b0ac40b6054cc5fa0ccbd9afd5ed4c" }, { "url": "https://git.kernel.org/stable/c/7a82fe67a9f4d7123d8e5ba8f0f0806c28695006" }, { "url": "https://git.kernel.org/stable/c/003d92c91cdb5a64b25a9a74cb8543aac9a8bb48" }, { "url": "https://git.kernel.org/stable/c/e5ee00607bbfc97ef1526ea95b6b2458ac9e7cb7" }, { "url": "https://git.kernel.org/stable/c/78533c4a29ac3aeddce4b481770beaaa4f3bfb67" }, { "url": "https://git.kernel.org/stable/c/5c3ca9cb48b51bd72bf76b8b05e24f3cd53db5e7" }, { "url": "https://git.kernel.org/stable/c/94edfdfb9505ab608e86599d1d1e38c83816fc1c" }, { "url": "https://git.kernel.org/stable/c/0c3057a5a04d07120b3d0ec9c79568fceb9c921e" } ], "title": "net_sched: Prevent creation of classes with TC_H_ROOT", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "title": "CVE Program Container", "references": [ { "url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html" }, { "url": "https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html" } ], "providerMetadata": { "orgId": "af854a3a-2127-422b-91ae-364da2661108", "shortName": "CVE", "dateUpdated": "2025-11-03T19:40:14.063Z" } } ] } }