CVE-2026-90076

A flaw was found in the Linux kernel's fq (Fair Queue) packet scheduler. An integer overflow can occur in the fq_init function when calculating quantum and initial_quantum values if a device is configured with an extremely large Maximum Transmission Unit (MTU). This overflow leads to a zero value for quantum, causing a credit-refill loop in fq_dequeue that results in a soft lockup. A local user with CAP_NET_ADMIN capabilities in a user namespace can exploit this vulnerability to cause a Denial of Service.

A flaw was found in the Linux kernel's fq (Fair Queue) traffic-control packet scheduler, rated moderate severity by Red Hat Product Security. In fq_init(), the quantum and initial_quantum values are computed as 2 and 10 times psched_mtu() without overflow checks. A local user with the CAP_NET_ADMIN capability in a user namespace can configure a network device with an extremely large MTU so that these 32-bit multiplications wrap to zero. The resulting zero quantum causes the credit-refill loop in fq_dequeue() to spin indefinitely while holding the qdisc lock, producing a kernel soft lockup and a local denial of service. Affected Red Hat products include the Red Hat Enterprise Linux 7, 8, 9, and 10 kernel and kernel-rt packages, the Red Hat In-Vehicle OS kernels, and the RHEL CoreOS kernels shipped in OpenShift Container Platform 4; for these products the fix is currently deferred to a later update, and the residual risk of that deferral is limited to availability, since exploitation requires local privileged access and results only in a denial of service with no impact to confidentiality or integrity. Red Hat Enterprise Linux 6 Extended Lifecycle Support is not affected because the vulnerable code is not present in that kernel.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.