CVE-2026-89752

A flaw was found in the Linux kernel's memory cgroup (memcg) component. When multiple file operations concurrently update memory.high or memory.max files in kernfs, a writer can continue reclaiming memory towards an outdated target. This can lead to an indefinite loop, causing a denial of service (DoS) by blocking the writer and repeatedly incrementing the Out-Of-Memory (OOM) event counter without terminating processes.

A LOW impact flaw was found in the Linux kernel memory cgroup (memcg) subsystem shipped in Red Hat Enterprise Linux and Red Hat OpenShift Container Platform (RHCOS). Because kernfs serializes file operations only per open file, separate open files can concurrently update the same cgroup memory.high or memory.max limit. A writer that has lowered a limit continues synchronous memory reclaim toward its stale target even after another writer raises or removes that limit; once reclaim retries are exhausted for memory.max, the writer can loop indefinitely, remaining blocked and repeatedly incrementing the OOM event counter without any process being killed. Exploitation requires local access with privileges to modify cgroup memory limits (such as root or CAP_SYS_ADMIN) and a specific concurrent write sequence, so the practical consequence is limited to a local denial of service; the issue was found through automated randomized testing rather than a reported production workload. Red Hat Enterprise Linux 7 (kernel and kernel-rt) is not affected because the vulnerable code is not present. Fixes for the affected Red Hat Enterprise Linux and OpenShift (RHCOS) streams are deferred because the flaw is rated LOW impact, and the residual risk is confined to an already-privileged local user blocking a process that writes cgroup memory limits. The Red Hat CVSS:3.1 score of 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, moderate) reflects the high availability impact, but Red Hat rates the overall impact LOW given the local privileged access requirement and the narrow trigger conditions.

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.