Linux Kernel Fix CVE-2024-50028: Prevent Thermal Zone Use-After-Free

Linux kernel maintainers have fixed a race-condition in the thermal subsystem that could let a thermal zone object be accessed after it was freed — a defect tracked as CVE-2024-50028 that carries a medium severity rating and is remedied by making thermal_zone_get_by_id take and return a proper device reference.

Background​

The Linux thermal subsystem exposes thermal zones (representing temperature sensors and cooling devices) to user space through sysfs and netlink interfaces. These zones are represented by kernel objects that must remain valid for the duration of any operation that reads or manipulates them. Over time, the kernel’s thermal stack has acquired multiple helpers and APIs; one of those functions, thermal_zone_get_by_id, is used by netlink and other callers to look up and return a pointer to a thermal zone based on an identifier.
A defect was discovered where the function returned a raw pointer to a thermal zone without incrementing the underlying device’s reference count in every relevant path. That meant a caller could receive a pointer to a zone that another thread or code path immediately freed, producing a classic use-after-free or dangling-pointer window that can manifest as kernel crashes or corruption — effectively an availability-impacting denial-of-service. The assigned CVE explains the fix as making thermal_zone_get_by_id grab a reference on the returned thermal-zone device using get_device under thermal_list_lock and updating the callers accordingly.

What changed upstream​

The technical fix, in plain terms​

• The upstream change makes thermal_zone_get_by_id obtain a device reference before returning the zone pointer.
• The change is implemented while holding thermal_list_lock so the returned pointer cannot be raced-away while the refcount is incremented.
• Callers were adjusted to expect that the returned zone carries a live reference and to release that reference using the kernel’s cleanup helpers (cleanup.h) when appropriate.

This is a defensive correctness change: the kernel must ensure object lifetime invariants are held any time a pointer is passed across contexts that may free or unregister the underlying object. The Linux CVE announcement and the stable commit messages identify the affected files as drivers/thermal/thermal_core.c, drivers/thermal/thermal_core.h and drivers/thermal/thermal_netlink.c and point to the stable commits that introduced the fix.

Where the fix appears in the kernel timeline​

The kernel project’s CVE notice documents the introduction and resolution timeline: the problematic code dates back to a change introduced in kernel 5.9 (commit 1ce50e7d408e), and the definitive fixes landed in the stable trees (fixed in 6.11.4 and in 6.12-rc3 with the referenced commits). If you track kernel changelogs or vendor backports, these commit identifiers are the canonical mapping to check for presence of the fix.

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Impact and risk assessment​

Primary impact: availability (denial-of-service)​

This vulnerability is an availability-first defect. The immediate observable consequence of a dangling thermal zone pointer — if dereferenced — is a kernel oops, WARN or panic, which can crash a running system or invalidate the ability to interact with the thermal subsystem until a reboot or patch is applied. Because the bug is rooted in a lifecycle/race condition rather than memory disclosure or code-execution primitives, the primary operational risk is reliably causing kernel instability and outages rather than elevating privileges or leaking secrets. Multiple vulnerability trackers classify the issue with a medium CVSS score emphasizing local attack vector and high availability impact.

Attack surface and exploitability​

• Vector: local — an attacker or untrusted workload that can interact with the thermal netlink or other thermal APIs on the host.
• Complexity: low-to-moderate — exploitation requires the ability to trigger the relevant netlink or thermal device flows at the same time another entity may unregister or free a zone. That can be achieved where untrusted processes run on the same kernel (containers, unprivileged processes on multi-user hosts, or guests on a host where guest interactions can influence thermal objects).
• Privilege required: low to moderate depending on specific syscalls and interfaces — on many systems netlink operations require some privilege, but automated or inadvertent device tear-down operations can be invoked by system services or hotplug events.

Because the exploit is local, single-user desktops are generally lower risk than multi‑tenant or cloud hosts, where an attacker may already have an ability to supply guest workloads or untrusted containers; in those environments the availability impact becomes a high-priority operational concern. This is the rationale behind the medium-level CVSS scoring and vendor advisories urging rapid kernel updates.

Who should worry most​

• Cloud hypervisor hosts and multi‑tenant virtualization nodes.
• Shared build farms, CI infrastructure, container hosts where untrusted code can be executed.
• Embedded or vendor-supplied Linux images that expose thermal netlink interfaces and receive updates on slow cadences.
• Security-conscious desktop deployments where uptime matters (e.g., workstations in critical control systems).

Windows-only users are not directly impacted by a Linux kernel bug, but Windows environments that interoperate with Linux VMs, WSL2, or vendor-maintained Linux images (for example, on Windows Server systems or Azure) should confirm whether any Linux artifacts they manage include the vulnerable kernel. Microsoft’s update guide lists this CVE so administrators should reconcile Linux kernel package status when Linux workloads are managed in Microsoft environments.

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Detection and hunting: what to look for​

Because this is a kernel lifetime/race defect, detection is primarily log- and telemetry-driven. Key signals include:

• Kernel oops traces or panic logs that include thermal subsystem symbols (for example calls into thermal_core or thermal_netlink).
• Messages arising from dereferences or WARN_ON triggered during thermal object access.
• Unexpected device-unregister sequences coincident with netlink activity.
• Reproducible crash traces when exercising thermal netlink queries concurrently with device removal or hotplug events.

Operationally, capture dmesg and kernel logs and search for thermal‑prefixed symbols in backtraces. Centralized logging that preserves kernel backtraces and panic dumps will make triage and validation far easier after deploying a patch. Distribution security advisories and the NVD/Ubuntu/Debian entries provide example file and function names that appear in published traces.

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Remediation and mitigation​

Definitive remediation​

• Install a kernel that includes the upstream fix — the upstream stable commits that address CVE-2024-50028 are present in kernel stable trees (the fix was merged into the stable releases referenced by vendor trackers). Use your distribution’s kernel updates or vendor-supplied images that include the commits.
• Reboot into the patched kernel — kernel-level fixes require a restart to take effect.
• Verify presence of the fix:
• Check your distribution’s package changelog or security advisory for CVE-2024-50028 or the stable commit IDs listed in upstream announcements.
• If you build your own kernel, confirm the commit is present in your source tree or that the drivers/thermal files reflect the reference-counting changes.

Short-term mitigations (if you cannot patch immediately)​

• Limit untrusted local access: restrict who can run processes that interact with netlink or thermal sysfs operations; remove or restrict container capabilities that permit direct netlink interactions where feasible.
• Harden service permissions: ensure only privileged, well-audited services can provoke device unregistrations or hotplug sequences that might race with netlink callers.
• Isolate vulnerable hosts: where patching is delayed, isolate multi-tenant hosts from public workloads or place them into maintenance windows until the kernel can be updated.

These short-term measures reduce the chance an untrusted actor can reproduce the race, but they are compensating controls only — they do not remove the vulnerability. The only complete remediation is a patched kernel and subsequent reboot.

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Operational checklist (step-by-step)​

• Inventory hosts running Linux kernels in the vulnerable range (introduced in 5.9 and fixed in stable 6.11.4 / 6.12-rc3 trees); gather uname -r and kernel package metadata.
• Consult your distro/vendor security tracker for package mappings to CVE-2024-50028 (Debian, Ubuntu, SUSE, Amazon Linux, Red Hat have entries describing fixed package versions or backport status).
• Apply vendor-provided kernel updates that include the upstream commits or upgrade to a kernel series that includes the fix.
• Schedule and perform reboots across your fleet in staged waves (pilot → staging → production).
• After reboot, validate with:
• grep through kernel logs for thermal oops traces
• smoke tests that exercise thermal netlink queries and device probe/unregister cycles in a controlled environment
• If vendor packages are not available for certain OEM images, escalate to the hardware/OEM vendor for a guidance and timeline; consider building a custom kernel with the stable commit as a last-resort mitigation (not recommended for general production without QA).

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Why this fix matters — analysis and context​

Strengths of the upstream response​

• Surgical and small: The fix is a minimal, correct lifetime-management change (grab a device reference and adjust callers), which makes it low-risk and straightforward to backport to stable branches.
• Clear observability: The fault mode (kernel oops/panic) is noisy and thus easier to detect when proper kernel logging is enabled; that helps defenders detect attempted abuse.
• Canonical remediation: The upstream kernel community provided commits and CVE mapping and the major distributions have tracked the CVE and started shipping patches or backports.

Remaining risks and caveats​

• Vendor/OEM lag: Embedded devices, vendor-maintained custom kernels, and long-tail images often lag upstream backports. These devices are at higher residual risk and will remain so until vendors issue updates.
• Local, but high-value attack: Although the vector is local, a local denial-of-service primitive is valuable in multi-tenant cloud environments; an attacker who can run untrusted workloads can repeatedly cause host instability.
• Assurance of backports: Not all distributions or vendors backport fixes identically; operators must verify package changelogs or commit metadata rather than assuming a kernel version number implies the presence of the fix.

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Practical guidance for WindowsForum readers​

Many readers use Windows machines in mixed Linux/Windows environments — developers, power users, admins who manage both worlds. Here’s how this matters practically:

• If you run Linux directly (dual‑boot or servers), prioritize installing the vendor kernel update and rebooting.
• If you run Linux as a VM on Windows hosts (Hyper‑V, VirtualBox, VMware), the guest kernel matters; verify and update guest kernels independently of the Windows host.
• If you use WSL2, check which kernel binary WSL is using (WSL can use a Microsoft-supplied kernel image or a custom kernel). Microsoft’s update guide lists Linux kernel-related CVEs that might be relevant to WSL-managed Linux artifacts — verify whether your WSL kernel was updated if you rely on sensitive workloads.
• If you use cloud images (Azure, AWS, etc., consult the cloud vendor’s image/AMI advisory to determine whether the distribution image you run was updated or requires a manual kernel update and reboot. Cloud images sometimes carry vendor-specific kernels that need separate tracking.

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Example detection commands and quick triage​

• Show kernel version:
• uname -r
• Check if thermal netlink/thermal modules are present:
• lsmod | grep thermal
• grep -i thermal /boot/config-$(uname -r)
• Search kernel logs for thermal oops/panic signatures:
• sudo journalctl -k | grep -i thermal
• sudo dmesg | grep -i thermal
• Confirm the kernel package changelog mentions CVE‑2024‑50028 or the upstream commit:
• zcat /usr/share/doc/linux-image-*/changelog.Debian.gz | grep -i 50028
• rpm -q --changelog kernel | grep -i thermal

These checks help you confirm exposure and validate remediation after patching.

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Final assessment and recommendations​

CVE‑2024‑50028 is a canonical example of a small coding oversight — missing an explicit reference-count increment — that escalates into a meaningful operational problem when the kernel attempts to access objects whose lifetime is not properly preserved. The fix is technically trivial but operationally crucial: deploying the kernel fix across exposed hosts prevents attackers or misbehaving local workloads from reliably crashing systems.
Action priorities for administrators and power users:

• Inventory Linux kernels and identify hosts with vulnerable kernels (introduced in 5.9, patched in stable 6.11.4/6.12-rc3 branches).
• Prioritize patching multi‑tenant hosts, public cloud hypervisors, and any systems where untrusted workloads run.
• Apply vendor kernel updates and reboot during scheduled maintenance windows.
• For slow-moving embedded or OEM images, escalate to vendors and apply compensating controls until a vendor-supplied kernel is available.

This CVE underlines a perennial lesson for systems operators: object lifetime invariants and proper reference counting are fundamental to kernel stability; small omissions can become large availability defects. The remediation path is straightforward — update the kernel — but the urgent operational work remains inventory, orchestration, and ensuring embedded/OEM images are validated and patched without undue delay.

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Source: MSRC Security Update Guide - Microsoft Security Response Center