CVE-2026-90076
Description
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.
Statement
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.
Mitigation
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.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.5 | N/A | N/A |
| Attack Vector | Local | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | Low | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (Memory); DoS: Instability
This weakness can generally lead to undefined behavior and therefore crashes. When the calculated result is used for resource allocation, this weakness can cause too many (or too few) resources to be allocated, possibly enabling crashes if the product requests more resources than can be provided.
Integrity
Technical Impact: Modify Memory
If the value in question is important to data (as opposed to flow), simple data corruption has occurred. Also, if the overflow/wraparound results in other conditions such as buffer overflows, further memory corruption may occur.
Confidentiality,Availability,Access Control
Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism
This weakness can sometimes trigger buffer overflows, which can be used to execute arbitrary code. This is usually outside the scope of the product's implicit security policy.
Availability,Other
Technical Impact: Alter Execution Logic; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)
If the overflow/wraparound occurs in a loop index variable, this could cause the loop to terminate at the wrong time - too early, too late, or not at all (i.e., infinite loops). With too many iterations, some loops could consume too many resources such as memory, file handles, etc., possibly leading to a crash or other DoS.
Access Control
Technical Impact: Bypass Protection Mechanism
If integer values are used in security-critical decisions, such as calculating quotas or allocation limits, integer overflows can be used to cause an incorrect security decision.
Frequently Asked Questions
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