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Fencer Vulns
no cvss —

CVE-2026-90076 json

net/sched: fq: add overflow bounds to quantum and initial quantum

published 2026-09-17 52 d ago modified 2026-10-30 10 d ago also EUVD-2026-81937

cvss
—
not scored
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 11%
public exploits
0
none known

Summary

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.

Patch / fix

  • Linux Linux 6.1.191, 6.6.160, 6.12.110, 6.18.52, 7.2.6, 7.3
  • linux Debian 13 6.12.111-1
  • linux Debian 14 7.2.6-1
  • linux-6.12 Debian 12 6.12.111-1~deb12u1

debian advisories DEBIAN-CVE-2026-90076

  • linux Ubuntu 26.04 LTS 7.0.0-42.42
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1016.17
  • linux-gcp Ubuntu 26.04 LTS 7.0.0-1016.18
  • linux-ibm Ubuntu 26.04 LTS 7.0.0-1017.17
  • linux-riscv Ubuntu 26.04 LTS 7.0.0-42.42.1
  • linux-oracle Ubuntu 26.04 LTS 7.0.0-1015.16
  • linux-hwe-7.0 Ubuntu 24.04 LTS 7.0.0-42.42~24.04.1
  • linux-oem-7.0 Ubuntu 26.04 LTS 7.0.0-1017.17

ubuntu advisories UBUNTU-CVE-2026-90076

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-source openSUSE Tumbleweed 7.2.7-1.1

opensuse advisories openSUSE-SU-2026:11880-1

  • kernel Azure Linux 3.0 6.6.161.1-1

azure linux advisories AZL-102791

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-90076 updated cvss 5.5

kernel: net/sched: fq: add overflow bounds to quantum and initial quantum

  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.21% chance of exploitation in the next 30 days, higher than 11% of all scored CVEs (FIRST EPSS, 2026-11-08).

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.