# CVE-2026-64374: sched/rt: Have RT_PUSH_IPI be default off for non PREEMPT_RT > Aggressive RT task migration causes high latency and potential denial of service on multi-CPU systems due to lock contention. - **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 25 Jul 2026 - **Updated:** 19 Oct 2026 - **Also known as:** AZL-93500, BELL-CVE-2026-64374, DEBIAN-CVE-2026-64374, GHSA-f9mw-ffqj-qm54, ROOT-OS-DEBIAN-12-CVE-2026-64374, ROOT-OS-UBUNTU-2204-CVE-2026-64374, UBUNTU-CVE-2026-64374 ## What is CVE-2026-64374? CVE-2026-64374 is a high-severity denial of service vulnerability in Linux kernel, published on 25 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description In the Linux kernel, the following vulnerability has been resolved: sched/rt: Have RT_PUSH_IPI be default off for non PREEMPT_RT RT migration is done aggressively. When a CPU schedules out a high priority RT task for a lower priority task, it will look to see if there's any RT tasks that are waiting to run on another CPU that is of higher priority than the task this CPU is about to run. If it finds one, it will pull that task over to the CPU and allow it to run there instead. Normally, this pulling is done by looking at the RT overloaded mask (rto) which contains all the CPUs in the scheduler domain with RT tasks that are waiting to run due to a higher priority RT task currently running on their CPU. The CPU that is about to schedule a lower priority task will grab the rq lock of the overloaded CPU and move the RT task from that CPU's runqueue to the local one and schedule the higher priority RT task. This caused issues when a lot of CPUs would schedule a lower priority task at the same time. They would all try to grab the same runqueue lock of the CPU with the overloaded RT tasks. Only the first CPU that got in will get that task. All the others would wait until they got the runqueue lock and see there's nothing to pull and do nothing. On systems with lots of CPUs, this caused a large latency (up to 500us) which is beyond what PREEMPT_RT is to allow. The solution to that was to create an RT_PUSH_IPI logic. When any CPU wanted to pull a task, instead of grabbing the runqueue lock of the overloaded CPU, it would start by sending an IPI to the overloaded CPU, and that IPI handler would have the CPU with the waiting RT task do a push instead. Then that handler would send an IPI to the next CPU with overloaded RT tasks, and so on. Note, after the first CPU starts this process, if another CPU wanted to do a pull, it would see that the process has already begun and would only increment a counter to have the IPIs continue again. The RT_PUSH_IPI solved the latency problem with PREEMPT_RT but could cause a new issue with non PREEMPT_RT. Namely, softirqs run in a threaded context on PREEMPT_RT but they can run in an interrupt context in non-RT. If an IPI lands on a CPU that has just woken up multiple RT tasks and the current CPU is running a non RT or a low priority RT task, instead of doing a push, it would simply do a schedule on that CPU. But if a softirq was also executing on this CPU, the schedule would need to wait until the softirq finished. Until then, the CPU would still be considered overloaded as there are RT tasks still waiting to run on it. A live lock occurred on a workload that was doing heavy networking traffic on a large machine where the softirqs would run 500us out of 750us. And it would also be waking up RT tasks, causing the RT pull logic to be constantly executed. When a softirq triggered on a CPU with RT tasks queued but not running yet, and the other CPUs would see this CPU as being overloaded, they would send an IPI over to it. The CPU would notice that the waiting RT tasks are of higher priority than the currently running task and simply schedule that CPU instead. But because the softirq was executing, before it could schedule, it would receive another IPI to do the same. The amount of IPIs would slow down the currently running softirq so much that before it could return back to task context, it would execute another softirq never allowing the CPU to schedule. This live locked that CPU. As RT_PUSH_IPI was created to help PREEMPT_RT, make it default off if PREEMPT_RT is not enabled. Weakness: CWE-667 (Improper Locking), CWE-835 (Loop with Unreachable Exit Condition) ## Which versions are affected by CVE-2026-64374? It affects 1 product. Products: Linux kernel. ## How do I fix CVE-2026-64374? Apply the vendor's patch. ## Is CVE-2026-64374 being exploited? There is no known exploitation of CVE-2026-64374 in the wild and no public exploit code. ## Other vulnerabilities in Linux kernel - [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild) - [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild) - [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild) - [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild) - [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-64374 and fix it if it is affected. What it is: CVE-2026-64374 is a high-severity denial of service vulnerability in Linux kernel, published on 25 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-64374 in the wild and no public exploit code. Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-64374/ (Markdown: https://insights.sbomify.com/CVE-2026-64374/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64374 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64374 - OSV: https://osv.dev/vulnerability/CVE-2026-64374 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-64374/ Summaries are generated and may contain mistakes; the official description above is the record.