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CVE-2026-90075— net/sched: fq_codel: clamp default quantum and mtu

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

以下是该 Linux 内核漏洞描述的中文翻译： 在 Linux 内核中，以下漏洞已被修复： net/sched: fq_codel: 限制默认量子值和 MTU 函数在设置 时未进行边界限制（clamping）。如果一个设备的 MTU 极大（例如，一个 max_mtu == 0 的 dummy 设备接受 MTU 为 2147483634），会导致 返回 0x80000000。该值在 中会使有符号的 溢出至 INT_MIN，从而导致无限循环和软死锁（soft lockup）。 修复方案是模拟 的行为，将值限制在 [25

AI Predicted 7.5 Difficulty: Moderate EPSS 0.21% · P10

Possible ATT&CK Techniques 1 AI

T1218 · System Binary Proxy Execution

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe< d315ee8a07fd1810880227319cf60e6cd925ef22 affected
4b549a2ef4bef9965d97cbd992ba67930cd3e0fe< a9a5b2943a00df2ab81a2209f31dd9e87016f120 affected
4b549a2ef4bef9965d97cbd992ba67930cd3e0fe< 3782067ec0d485628b6f1f9ede3eeeb4f611fcf2 affected
4b549a2ef4bef9965d97cbd992ba67930cd3e0fe< 397e2b1f71d9f15b8b4e47d24eb620e4dff8878d affected
4b549a2ef4bef9965d97cbd992ba67930cd3e0fe< 324f86806673ae4a55f66d28db84577f46f615e1 affected
4b549a2ef4bef9965d97cbd992ba67930cd3e0fe< dfb4b61db886917244284b18b44b23d2254b82c2 affected
4b549a2ef4bef9965d97cbd992ba67930cd3e0fe< 9f499e5827fdb6d7fdb46a7ce731852f6b1a1bb9 affected
4b549a2ef4bef9965d97cbd992ba67930cd3e0fe< d9ebd8f9aa8b2773235889cb903fafd61f2d8585 affected
… +10 more rows
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I. Basic Information for CVE-2026-90075

Vulnerability Information
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Vulnerability Title
net/sched: fq_codel: clamp default quantum and mtu
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: net/sched: fq_codel: clamp default quantum and mtu fq_codel_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without clamping. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000, which overflows the signed flow->deficit to INT_MIN in fq_codel_dequeue(), causing an infinite loop and soft lockup. Emulate fq_codel_change() and constrain to [256, FQ_CODEL_QUANTUM_MAX]. The same unclamped psched_mtu() is assigned to q->cparams.mtu a bit below, and fq_codel_change() never updates it. codel_should_drop() tests "*backlog <= params->mtu"; with mtu == 0x80000000 (~2 GiB) and the default 32 MiB memory_limit, the test is always true, so CoDel is silently and completely disabled (no drops, no ECN). Declare a single clamped mtu and assign both q->quantum and q->cparams.mtu from it, which also removes the double psched_mtu() call. Conditions to recreate the bug: a device whose MTU (plus hard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy device with max_mtu == 0 accepting MTU 2147483634). Requires CAP_NET_ADMIN in a user namespace.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 4b549a2ef4bef9965d97cbd992ba67930cd3e0fe ~ d315ee8a07fd1810880227319cf60e6cd925ef22 -
Linux Linux 3.5 -

II. Public POCs for CVE-2026-90075

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III. Intelligence Information for CVE-2026-90075

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Patches & Fixes for CVE-2026-90075 (8)

Same Patch Batch · Linux · 2026-09-17 · 600 CVEs total

CVE-2026-90173 9.8 CRITICAL smb: smbdirect: free completion queues with ib_free_cq()
CVE-2026-92489 9.8 CRITICAL xfrm: Fix skb double-free in xfrm_dev_direct_output()
CVE-2026-90104 9.8 CRITICAL NFSv4.1: zero referring call lists before decoding
CVE-2026-90235 9.8 CRITICAL sunrpc: xprtsock: annotate shared socket callbacks with READ_ONCE/WRITE_ONCE
CVE-2026-90151 9.8 CRITICAL NFSv4: remove callback IDR entry on client allocation failure
CVE-2026-90110 9.4 CRITICAL inetpeer: randomize RB-tree node comparison using SipHash
CVE-2026-90414 9.1 CRITICAL IB/isert: reject PDUs declaring more data than was received
CVE-2026-90413 9.1 CRITICAL IB/isert: reject login PDUs declaring more data than was received
CVE-2026-90230 9.1 CRITICAL nvmet: fix heap out-of-bounds read in nvmet_auth_negotiate()
CVE-2026-90381 8.8 HIGH wifi: mt76: fix handling channel context with different bands in mt76_switch_vif_chanctx()
CVE-2026-90329 8.8 HIGH HID: synchronize input before cleaning up a failed probe
CVE-2026-90162 8.8 HIGH ksmbd: defer publishing granted locks to prevent UAF/double-free race
CVE-2026-90357 8.8 HIGH wifi: mt76: mt7915: unlink TWT flow if the MCU rejects the agreement
CVE-2026-90367 8.8 HIGH wifi: mt76: mt7996: hold dev->mt76.mutex while disabling tx worker in SER
CVE-2026-90371 8.8 HIGH wifi: mt76: fix RXDMAD_C buffer recycling race
CVE-2026-93042 8.8 HIGH dmaengine: dw-edma: Terminate all descriptors without callbacks
CVE-2026-90425 8.8 HIGH iommu/tegra241-cmdqv: Require exactly one Stream ID for a vSID
CVE-2026-90240 8.8 HIGH iommu/vt-d: Flush context cache with correct SID when tearing down aliases
CVE-2026-90379 8.8 HIGH wifi: mt76: mt7921: Add PCIe AER handler support to prevent system crash
CVE-2026-90256 8.8 HIGH Bluetooth: L2CAP: use proto_lock for l2cap_data to fix l2cap_disconn_ind

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IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-90075

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