{"cve":"CVE-2025-38457","nvd":{"published":"2025-07-25T16:15:31.403","modified":"2026-06-17T09:16:53.663","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Abort __tc_modify_qdisc if parent class does not exist\n\nLion's patch [1] revealed an ancient bug in the qdisc API.\nWhenever a user creates/modifies a qdisc specifying as a parent another\nqdisc, the qdisc API will, during grafting, detect that the user is\nnot trying to attach to a class and reject. However grafting is\nperformed after qdisc_create (and thus the qdiscs' init callback) is\nexecuted. In qdiscs that eventually call qdisc_tree_reduce_backlog\nduring init or change (such as fq, hhf, choke, etc), an issue\narises. For example, executing the following commands:\n\nsudo tc qdisc add dev lo root handle a: htb default 2\nsudo tc qdisc add dev lo parent a: handle beef fq\n\nQdiscs such as fq, hhf, choke, etc unconditionally invoke\nqdisc_tree_reduce_backlog() in their control path init() or change() which\nthen causes a failure to find the child class; however, that does not stop\nthe unconditional invocation of the assumed child qdisc's qlen_notify with\na null class. All these qdiscs make the assumption that class is non-null.\n\nThe solution is ensure that qdisc_leaf() which looks up the parent\nclass, and is invoked prior to qdisc_create(), should return failure on\nnot finding the class.\nIn this patch, we leverage qdisc_leaf to return ERR_PTRs whenever the\nparentid doesn't correspond to a class, so that we can detect it\nearlier on and abort before qdisc_create is called.\n\n[1] https://lore.kernel.org/netdev/d912cbd7-193b-4269-9857-525bee8bbb6a@gmail.com/","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":[],"references":["https://git.kernel.org/stable/c/23c165dde88eac405eebb59051ea1fe139a45803","https://git.kernel.org/stable/c/25452638f133ac19d75af3f928327d8016952c8e","https://git.kernel.org/stable/c/4c691d1b6b6dbd73f30ed9ee7da05f037b0c49af","https://git.kernel.org/stable/c/8ecd651ef24ab50123692a4e3e25db93cb11602a","https://git.kernel.org/stable/c/90436e72c9622c2f70389070088325a3232d339f"],"products":["debian:debian_linux","linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:05:46.678065081+00:00"},"epss":{"cve":"CVE-2025-38457","score":0.00196,"percentile":0.09385,"date":"2026-10-31"},"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."]}