{"id":"CVE-2025-37798","state":"PUBLISHED","title":"codel: remove sch->q.qlen check before qdisc_tree_reduce_backlog()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ncodel: remove sch->q.qlen check before qdisc_tree_reduce_backlog()\n\nAfter making all ->qlen_notify() callbacks idempotent, now it is safe to\nremove the check of qlen!=0 from both fq_codel_dequeue() and\ncodel_qdisc_dequeue().","publishedAt":"2025-05-02T14:16:02.623Z","updatedAt":"2026-10-15T21:51:59.989Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux 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remove sch->q.qlen check before qdisc_tree_reduce_backlog()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ncodel: remove sch->q.qlen check before qdisc_tree_reduce_backlog()\n\nAfter making all ->qlen_notify() callbacks idempotent, now it is safe to\nremove the check of qlen!=0 from both fq_codel_dequeue() 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- The vulnerable state is created and triggered through tc/rtnetlink qdisc configuration (RTM_NEWQDISC/RTM_NEWTCLASS/RTM_DELTCLASS) plus locally generated traffic over a loopback or veth device. There is no remote entry point into the qdisc class hierarchy setup.\nAC:L - The attacker controls every input: the qdisc hierarchy, CoDel's target/interval (unvalidated in codel_change()), the device MTU that defeats the backlog>mtu drop guard, the traffic that fills and empties the queue, and the moment the class is deleted. The inconsistent active-but-empty class state persists indefinitely, so no race window must be won.\nPR:L - Configuring qdiscs requires CAP_NET_ADMIN, but rtnetlink checks it via sk_ns_capable(sk, net->user_ns, CAP_NET_ADMIN), which any unprivileged local user obtains inside a `unshare -Urn` user+network namespace. Per kernel scoring guidance, tc/qdisc reachable through user namespaces is Low, not High.\nUI:N - The attacker performs every step — qdisc setup, traffic generation, and class deletion — within their own namespace. No victim action or interaction is needed.\nS:U - The corruption is confined to kernel heap objects and scheduler data structures managed by the same kernel security authority. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - The freed drr_class/qfq_class/hfsc_class remains linked in the parent's active list and rbtrees; after heap reclaim the attacker controls the object contents and the traversals read kernel pointers back out of it, yielding an arbitrary-read primitive and kernel address disclosure. Per guidance, use-after-free is High.\nI:H - Subsequent list_del/list_add and rb_erase operations write through pointers stored in the freed object, and drr_dequeue()/agg_dequeue() perform an indirect call via cl->qdisc->ops->peek() on reclaimed memory, giving a write primitive and control-flow hijack suitable for full privilege escalation.\nA:H - Even without successful exploitation, the dangling class in the active list/rbtree causes list and red-black-tree corruption and dereference of poisoned or freed pointers, producing a kernel oops or panic that can be triggered repeatedly by an unprivileged user."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T11:57:37.129Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"5.4.297"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"5.10.241"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"5.15.190"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"6.1.135"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"6.6.88"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"6.12.24"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"6.13.12"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"6.14.3"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.5","versionEndExcluding":"6.15"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CVE Program Container","references":[{"url":"https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html"},{"url":"https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html"}],"providerMetadata":{"shortName":"CVE","orgId":"af854a3a-2127-422b-91ae-364da2661108","dateUpdated":"2025-11-03T19:55:29.865Z"}},{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2025-37798","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-15T21:45:14.746981Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-15T21:51:59.989Z"}}]}}}