A memory-leak bug in the Linux kernel’s UBI driver — tracked as CVE‑2024‑25740 — allows repeated use of the UBI_IOCATT path to accumulate unreleased kernel objects because the kobject name (kobj->name) is not freed on error paths, producing a sustained or persistent availability impact that vendors classify as a medium‑severity, availability‑focused vulnerability.
The UBI (Unsorted Block Images) driver is part of the MTD (Memory Technology Device) subsystem and is widely used on embedded devices and appliances that must manage raw flash volumes. The bug described by CVE‑2024‑25740 sits in drivers/mtd/ubi/attach.c and specifically in the code path that handles the UBI_IOCATT ioctl (the attach operation). Multiple vulnerability trackers reproduce the core summary: a kobject name allocated during attach is not released on certain failure or error return paths, leaving a small kernel allocation unreferenced. Over repeated triggers this leak can grow into a denial‑of‑service condition. Why this matters operationally: kernel leaks are not immediate remote‑RCE vectors, but they are high impact in long‑uptime systems, multi‑tenant hosts, CI/test farms and embedded appliances where repeated attach/detach cycles or automated provisioning can repeatedly exercise the vulnerable path and exhaust kernel memory or slab resources, triggering OOMs and service outages. Multiple distributors and trackers therefore emphasize the availability impact as the primary concern.
Source: MSRC Security Update Guide - Microsoft Security Response Center
Background / Overview
The UBI (Unsorted Block Images) driver is part of the MTD (Memory Technology Device) subsystem and is widely used on embedded devices and appliances that must manage raw flash volumes. The bug described by CVE‑2024‑25740 sits in drivers/mtd/ubi/attach.c and specifically in the code path that handles the UBI_IOCATT ioctl (the attach operation). Multiple vulnerability trackers reproduce the core summary: a kobject name allocated during attach is not released on certain failure or error return paths, leaving a small kernel allocation unreferenced. Over repeated triggers this leak can grow into a denial‑of‑service condition. Why this matters operationally: kernel leaks are not immediate remote‑RCE vectors, but they are high impact in long‑uptime systems, multi‑tenant hosts, CI/test farms and embedded appliances where repeated attach/detach cycles or automated provisioning can repeatedly exercise the vulnerable path and exhaust kernel memory or slab resources, triggering OOMs and service outages. Multiple distributors and trackers therefore emphasize the availability impact as the primary concern. The technical root cause — how kobj->name gets orphaned
What the code does (high level)
When the kernel creates sysfs entries or registers a kobject it often needs to build a name string for the object and hand that name into the kobject lifetime machinery. To do that the UBI attach path allocates a formatted name (via kernel helpers such as kvasprintf/kstrdup or equivalent) then assigns that pointer to kobj->name before calling kobject_add/kobject_init_and_add. If kobject registration succeeds, the kobject subsystem assumes ownership of name and will free it at the appropriate time; if registration fails, the kernel code must explicitly free any temporary memory it allocated. The CVE arises because, on some error/early‑return paths after the name is set, the code exits without freeing kobj->name — leaving the allocation orphaned. Multiple trackers and the CVE metadata repeat that the bug is a missing release of kobj->name in the drivers/mtd/ubi/attach.c path.Why that pattern leaks memory
Kernel allocations used as kobject names are small but persistent: they live until either the kobject is released or the allocator reclaims them through an explicit free. If a kobject name is set but the kobject is never fully registered, or if subsequent code frees other resources but forgets to free the name, the name pointer becomes unreachable and kmemleak (or the allocator) reports it as an unreferenced object. Repeating the attach ioctl or cycling the module can create dozens or hundreds of these small, leaked allocations, increasing slab usage and eventually provoking kernel memory pressure that can cascade to OOM kills or panics. This pattern is a classic "missing release" / CWE‑401 case in low‑level C code.Observability and reproduction (what researchers and maintainers saw)
Investigators reproduce these classes of leaks with tools such as kmemleak (the kernel leak detector), which reports unreferenced allocations and provides backtraces that show where the allocation originated. Public reproducer notes for similar kobject leakage bugs typically demonstrate a simple attach path invocation (for UBI that is often achieved via userspace tools such as ubiattach or by issuing the UBI_IOCATT ioctl) that leaves a small allocation reported by kmemleak. The diagnostic stack traces from kmemleak are low‑noise and make reproducing and confirming the leak straightforward in a test environment. Vendors and tracker entries cite kmemleak traces as diagnostic evidence used to identify this exact flaw class.Severity, exploitability and realistic risk profile
- Severity: most CNAs and distributors assign a medium base rating (commonly CVSS 3.x ≈ 5.5) because the vector is local, complexity is low, privileges required are low, and the primary impact is availability. The canonical vector emphasized across advisories is AV:L/AC:L/PR:L/UI:N with High availability impact.
- Exploitability: the vulnerability is local‑only (not remotely exploitable by default). An attacker needs the ability to call UBI_IOCATT or otherwise cause the driver attach path to run repeatedly. On multi‑tenant hosts that allow unprivileged or containerized actors to interact with device ioctls, the attack surface grows. In most mainstream server deployments the required prerequisites are restricted (root or privileged access), but in embedded appliances or poorly isolated containers the risk is higher.
- Impact: the CVE metadata and vendor advisories all emphasize availability — repeated exploitation yields progressive kernel memory consumption that can lead to service instability, OOM killers, and even host reboots. Some advisories note that even small per‑trigger leaks become critical in long‑uptime systems or automated testbeds where attach operations are frequent. There is no authoritative public proof‑of‑concept showing privilege escalation or arbitrary code execution using only this leak; the practical and observed impact is denial of service.
Affected versions and vendor response
- Upstream boundary: public trackers map the vulnerable range to kernel versions up to and including 6.7.4 (that is, kernels built from upstream trees without the subsequent stable fix are in scope). Mitigation commits have since been accepted into the stable kernel series; distribution updates and backports follow at differing cadences.
- Distribution mapping: major distributions and security trackers (Debian, Ubuntu, SUSE, others) have recorded the CVE and listed package‑level status. Debian’s security tracker shows specific package mappings and notes the stable backport targets; SUSE and Ubuntu provide advisories and CVSS assessments that reflect the operational impact. Always consult your distribution security tracker for the exact fixed package version for your release.
- Patch status and fixes: the upstream fix is a small clean‑up that ensures the allocated name is freed on all error/early‑return paths (defensive cleanup). Because the change is localized and low‑risk, kernel maintainers recommend backporting to stable branches; distributions have accordingly shipped fixed kernels on a rolling basis. If a vendor marks a specific kernel package as fixed, confirm the package changelog references the upstream commit or lists CVE‑2024‑25740 explicitly before declaring remediation complete.
Detection, mitigation and recommended operations playbook
Immediate verification and detection
- Run kmemleak in a test environment that reproduces the attach path. If you can exercise the UBI_IOCATT ioctl (or run ubiattach against a test MTD device), kmemleak will report unreferenced allocations with a backtrace. That trace is the canonical evidence used during public triage.
- Monitor kernel slab and memory telemetry on long‑uptime hosts and multi‑tenant systems. Look for sustained growth in kernel slab usage or repeated OOM events coincident with device‑attach operations. Add alerts for kernel memory pressure spikes.
- Audit which hosts allow access to UBI ioctls or permit automated attach cycles from untrusted workloads. Inventory kernel config and module usage (lsmod, /sys/bus/mtd, /proc/config.gz) to identify at‑risk systems.
Definitive remediation
- Install vendor‑supplied patched kernels that include the upstream stable commit for CVE‑2024‑25740 and reboot into them. Kernel fixes require a full reboot to take effect. Confirm the package changelog references the upstream patch or lists CVE‑2024‑25740.
- For vendors that backport the fix, confirm the backport appears in your distribution’s kernel package before declaring remediation complete. Distribution backport cadence varies — embedded vendor kernels and OEM images are often the slowest to be updated.
Compensating controls (temporary, pre‑patch)
- Restrict local access: tighten who can open or ioctl MTD/UBI devices. Use file permissions, SELinux/AppArmor policies, and container capability restrictions to prevent untrusted processes from invoking UBI attach operations.
- Blacklist/unload the UBI driver on hosts that do not require it. If UBI functionality is not needed on a host, blacklisting the module (modprobe.blacklist=ubi or rebuilding a kernel without UBI) removes the exposure surface.
- Isolate high‑risk hosts (CI runners, testbeds, multi‑tenant build machines) until patches can be applied. Prevent untrusted users or containers from running privileged device‑management operations.
Testing and rollout guidance
- Stage the patched kernel in a pilot ring and run representative workloads, including attach/detach cycles that previously exercised the path. Validate that kmemleak or equivalent instrumentation no longer reports the orphaned allocations.
- Use centralized kernel logging, kdump / vmcore capture and persistent journal so any unexpected oops traces are caught and preserved for forensics; kernel oops messages are transient and lost across reboots unless persisted.
- For embedded device fleets where vendor updates are delayed, coordinate with the hardware/OEM vendor for an official image or apply a vendor‑provided hotpatch mechanism when available. If no vendor update will be issued, consider network isolation and operation changes that limit repeated attach operations as a long‑term mitigation.
Operational advice by environment
Cloud and multi‑tenant hosts
Priority: high. Shared infrastructure and multi‑tenant virtualization increase the blast radius if a guest or tenant can trigger local ioctls or otherwise cause attach operations. Inventory kernels in cloud images and any vendor‑supplied host OS artifacts (for example, Azure Linux or vendor images) and confirm vendor attestations or VEX/CSAF attestations that map CVE‑2024‑25740 to product binaries. If a cloud provider issues its own advisory, follow that guidance and schedule a rolling reboot to the patched kernel.Embedded devices and appliances
Priority: highest. The long tail of embedded images and vendor kernels often lags upstream; these systems frequently include UBI/MTD code and are commonly exposed to attach cycles by provisioning scripts or device provisioning services. Work with the OEM to obtain a patched kernel image; where that is impossible, harden the device by limiting local access and network exposure.Developer workstations, CI runners, test farms
Priority: medium‑high. These environments frequently load and unload modules and run reproduce scripts — exactly the scenario that turns small leaks into large operational problems. Apply patches early and consider temporarily restricting who can run jobs that exercise device attach paths until the kernel is updated. Use ephemeral test hosts where possible.Critical analysis — strengths of the response and remaining risks
Strengths
- The upstream patch is small and surgical — a focused cleanup to free allocated resources on all exit paths. That constrained scope significantly reduces the risk of functional regressions and makes the change easy to review and backport into stable kernels. Vendor packaging and distribution trackers reflect this, and many distros have already produced fixed packages.
- The defect is a classic, well‑understood class (missing free) and is detectable with deterministic kernel instrumentation (kmemleak), so operators have reliable tools to validate both the problem and the fix. That makes rollout verification straightforward in test environments.
Residual risks and caveats
- Backport variance: distribution and vendor backports do not all arrive at the same time. Embedded and OEM kernels often lag and must be inventoried separately. Operators must not rely on kernel version numbers alone; they should confirm fixed commit IDs or package changelogs.
- Attack surface assumptions: while the bug is local by design, misconfigurations (privileged containers, cap‑rich containers, exposed device nodes) can broaden the exposure. Administrators should treat access controls around device ioctls as part of the remediation posture.
- Chained‑exploit possibility: though this bug alone is a leak (not a UAF or overwrite), kernel resource‑lifetime bugs can sometimes participate in chained exploit scenarios when combined with other bugs. No public proof exists that CVE‑2024‑25740 has been used for privilege escalation, but uncertainty remains inherent with kernel defects; treat escalation as theoretical but not impossible.
Practical checklist for administrators (concise)
- Inventory: identify hosts that include UBI/MTD (grep kernel config; check /sys/bus/mtd and lsmod).
- Confirm: check your distribution security tracker or vendor advisory for the exact kernel package version that includes the CVE‑2024‑25740 fix and verify changelog/commit ID.
- Stage: deploy patched kernel to a pilot group and run attach/detach soak tests; validate kmemleak no longer shows orphaned allocations.
- Rollout: schedule maintenance windows to roll patched kernels into production; ensure kdump/vmcore is enabled to retain crash dumps during the transition.
- Compensate: if you cannot patch immediately, restrict device ioctl access, blacklist the UBI driver where unused, and isolate multi‑tenant hosts.
Conclusion
CVE‑2024‑25740 is a targeted, correctness bug in the UBI attach path where a kobject name is not reliably freed. Its operational significance comes from the classic leak pattern: repeated triggering leads to progressive kernel memory growth and availability loss. The fix is straightforward and low risk — a defensive cleanup — and has been merged into stable kernels and incorporated into distribution advisories. The correct operational response is clear: inventory your kernel artifacts, apply vendor‑supplied kernel updates that include the upstream patch, reboot into the patched kernel, and in the meantime restrict local access to UBI attach operations on hosts that cannot be immediately updated. Detection is practical (kmemleak and slab monitoring), and compensating controls are available for constrained environments, but the ultimate remedy is an updated kernel image validated against your vendor’s changelog and the upstream commit set.Source: MSRC Security Update Guide - Microsoft Security Response Center
