{"cve":"CVE-2025-21971","nvd":{"published":"2025-04-01T16:15:28.440","modified":"2026-10-15T22:18:12.710","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":["CWE-835"],"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"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:00:57.946988208+00:00"},"epss":{"cve":"CVE-2025-21971","score":0.00227,"percentile":0.13377,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}