CVE-2026-90076

In the Linux kernel, the following vulnerability has been resolved: net/sched: fq: add overflow bounds to quantum and initial quantum fq_init() computes quantum = 2 * psched_mtu() and initial_quantum = 10 * psched_mtu() with no overflow check. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000; the 2 * and 10 * multiplications wrap to 0 in 32-bit arithmetic, so q->quantum == 0. Then in fq_dequeue() the credit-refill loop adds 0 to f->credit (which stays <= 0) and goto begin loops forever under the qdisc lock, creating a soft lockup. Clamp psched_mtu() to [1, 1 << 20] before multiplying so the product cannot wrap, then cap the result at 1 << 20, matching the bound already enforced on TCA_FQ_QUANTUM in fq_change(). Conditions to recreate the bug: a device whose MTU (plus hard_header_len) is large enough that 2 * psched_mtu() wraps (e.g. a dummy device with max_mtu == 0 accepting MTU 2147483634). Requires CAP_NET_ADMIN in a user namespace.

CVSS

No CVSS.

References

Link	Resource
https://git.kernel.org/stable/c/709f34f7c28dc4dd6c40343d101850f11e172312
https://git.kernel.org/stable/c/d16dac3925be95ad46e986d4b139c9898b6e227f
https://git.kernel.org/stable/c/e35acd56f244d94355f9ab237c2ecc8fba5e6f04
https://git.kernel.org/stable/c/f6b3e3848a5fca63438984acd6d9eceac80814c1

Configurations

No configuration.

History

17 Sep 2026, 17:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-09-17 17:16

Updated : 2026-09-17 17:16

NVD link : CVE-2026-90076

Mitre link : CVE-2026-90076

CVE.ORG link : CVE-2026-90076

JSON object : View

Products Affected

No product.

CWE

No CWE.

{"id": "CVE-2026-90076", "cveTags": [], "metrics": {}, "affected": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "affectedData": [{"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "product": "Linux", "versions": [{"status": "affected", "version": "afe4fd062416b158a8a8538b23adc1930a9b88dc", "lessThan": "d16dac3925be95ad46e986d4b139c9898b6e227f", "versionType": "git"}, {"status": "affected", "version": "afe4fd062416b158a8a8538b23adc1930a9b88dc", "lessThan": "f6b3e3848a5fca63438984acd6d9eceac80814c1", "versionType": "git"}, {"status": "affected", "version": "afe4fd062416b158a8a8538b23adc1930a9b88dc", "lessThan": "e35acd56f244d94355f9ab237c2ecc8fba5e6f04", "versionType": "git"}, {"status": "affected", "version": "afe4fd062416b158a8a8538b23adc1930a9b88dc", "lessThan": "709f34f7c28dc4dd6c40343d101850f11e172312", "versionType": "git"}], "programFiles": ["net/sched/sch_fq.c"], "defaultStatus": "unaffected"}, {"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "product": "Linux", "versions": [{"status": "affected", "version": "3.12"}, {"status": "unaffected", "version": "0", "lessThan": "3.12", "versionType": "semver"}, {"status": "unaffected", "version": "6.12.110", "versionType": "semver", "lessThanOrEqual": "6.12.*"}, {"status": "unaffected", "version": "6.18.52", "versionType": "semver", "lessThanOrEqual": "6.18.*"}, {"status": "unaffected", "version": "7.2.6", "versionType": "semver", "lessThanOrEqual": "7.2.*"}, {"status": "unaffected", "version": "7.3-rc1", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*"}], "programFiles": ["net/sched/sch_fq.c"], "defaultStatus": "affected"}]}], "published": "2026-09-17T17:16:56.820", "references": [{"url": "https://git.kernel.org/stable/c/709f34f7c28dc4dd6c40343d101850f11e172312", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/d16dac3925be95ad46e986d4b139c9898b6e227f", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/e35acd56f244d94355f9ab237c2ecc8fba5e6f04", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/f6b3e3848a5fca63438984acd6d9eceac80814c1", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "vulnStatus": "Received", "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fq: add overflow bounds to quantum and initial quantum\n\nfq_init() computes quantum = 2 * psched_mtu() and initial_quantum = 10 *\npsched_mtu() with no overflow check. A device with a huge MTU (e.g. dummy\nwith max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return\n0x80000000; the 2 * and 10 * multiplications wrap to 0 in 32-bit\narithmetic, so q->quantum == 0. Then in fq_dequeue() the credit-refill\nloop adds 0 to f->credit (which stays <= 0) and goto begin loops\nforever under the qdisc lock, creating a soft lockup.\n\nClamp psched_mtu() to [1, 1 << 20] before multiplying so the product\ncannot wrap, then cap the result at 1 << 20, matching the bound already\nenforced on TCA_FQ_QUANTUM in fq_change().\n\nConditions to recreate the bug: a device whose MTU (plus\nhard_header_len) is large enough that 2 * psched_mtu() wraps (e.g. a\ndummy device with max_mtu == 0 accepting MTU 2147483634). Requires\nCAP_NET_ADMIN in a user namespace."}], "lastModified": "2026-09-17T17:16:56.820", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}