{"id":"CVE-2026-90075","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq_codel: clamp default quantum and mtu\n\nfq_codel_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without\nclamping","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq_codel: clamp default quantum and mtu\n\nfq_codel_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without\nclamping. A device with a huge MTU (e.g. dummy …","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe < d315ee8a07fd1810880227319cf60e6cd925ef22","Linux >= 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe < a9a5b2943a00df2ab81a2209f31dd9e87016f120","Linux >= 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe < 3782067ec0d485628b6f1f9ede3eeeb4f611fcf2","Linux >= 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe < 397e2b1f71d9f15b8b4e47d24eb620e4dff8878d","Linux >= 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe < 324f86806673ae4a55f66d28db84577f46f615e1","Linux >= 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe < dfb4b61db886917244284b18b44b23d2254b82c2","Linux >= 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe < 9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9","Linux >= 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe < d9ebd8f9aa8b2773235889cb903fafd61f2d8585","Linux 3.5"],"published":"2026-09-17","updated":"2026-09-17","sourceUpdated":"2026-09-17T17:16:56.670","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-90075","references":[{"url":"https://git.kernel.org/stable/c/324f86806673ae4a55f66d28db84577f46f615e1","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/3782067ec0d485628b6f1f9ede3eeeb4f611fcf2","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/397e2b1f71d9f15b8b4e47d24eb620e4dff8878d","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/a9a5b2943a00df2ab81a2209f31dd9e87016f120","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/d315ee8a07fd1810880227319cf60e6cd925ef22","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/d9ebd8f9aa8b2773235889cb903fafd61f2d8585","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/dfb4b61db886917244284b18b44b23d2254b82c2","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"tags":["nvd","cve.org"],"ingestedAt":"2026-09-17T16:21:47.897Z","epss":0.00211,"epssPercentile":0.1158,"slug":"CVE-2026-90075","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq_codel: clamp default quantum and mtu\n\nfq_codel_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without\nclamping. A device with a huge MTU (e.g. dummy with max_mtu == 0\naccepting MTU 2147483634) makes psched_mtu() return 0x80000000, which\noverflows the signed flow->deficit to INT_MIN in fq_codel_dequeue(),\ncausing an infinite loop and soft lockup. Emulate fq_codel_change()\nand constrain to [256, FQ_CODEL_QUANTUM_MAX].\n\nThe same unclamped psched_mtu() is assigned to q->cparams.mtu a bit\nbelow, and fq_codel_change() never updates it. codel_should_drop()\ntests \"*backlog <= params->mtu\"; with mtu == 0x80000000 (~2 GiB) and\nthe default 32 MiB memory_limit, the test is always true, so CoDel is\nsilently and completely disabled (no drops, no ECN). Declare a single\nclamped mtu and assign both q->quantum and q->cparams.mtu from it,\nwhich also removes the double psched_mtu() call.\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy\ndevice with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}