CVE-2023-53410: Linux ULPI Debugfs Memory Leak Patch Explained

A small but real Linux-kernel vulnerability, tracked as CVE‑2023‑53410, fixes a memory leak in the USB ULPI driver where a missed dput after a debugfs_lookup call could let kernel memory accumulate over time — the practical impact is availability (resource exhaustion) rather than privilege escalation, and the upstream fix is a small, defensive cleanup that replaces the manual lookup/forget sequence with the safer debugfs_lookup_and_remove helper.

Background / Overview​

USB drivers in the Linux kernel interact with various debug and device introspection helpers; one common helper is debugfs, used to expose runtime state to administrators and developers. Calling debugfs_lookup returns a dentry-like object that must be released with dput when it is no longer needed; failing to do so leaves a reference held in kernel memory, producing a leak that accumulates when the code path is exercised repeatedly. CVE‑2023‑53410 documents exactly this class of bug inside the ULPI (USB Low‑Pin Count Interface) subsystem. The vulnerability was published in September 2025 and assigned a medium operational severity by multiple vendors and trackers; the common theme across advisories is that the impact is availability — repeated triggering of the defective code path can increase kernel slab usage and eventually impair system stability. Major Linux distribution trackers (Debian, Ubuntu) and vulnerability aggregators reflect the fix and map it into vendor package updates.

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Technical anatomy — what went wrong​

The bug in plain language​

• The ULPI code called debugfs_lookup to find a debugfs entry.
• The code path that handled the failed or alternate outcomes neglected to call dput on the returned object.
• Over many repetitions this omission leaves allocations referenced inside kernel structures and not freed, producing a memory leak (CWE‑401 — missing release of memory after effective lifetime).

This is not a classic memory‑corruption primitive (use‑after‑free or arbitrary write). Instead it is a lifecycle / cleanup omission: the kernel retains references to debugfs objects that should be released and thus consumes kernel-memory over time. The leak is observable in long‑running or heavily exercised systems — device lab test rigs, CI runners, automated attach/detach workflows, or multi‑tenant appliances where the ULPI path is regularly exercised.

Why debugfs_lookup matters​

debugfs_lookup returns a pointer-like object that increments a reference count. Kernel callers are required to call dput after they finish using the lookup result. A correct usage pattern requires symmetrical acquisition and release on success and on all error paths; missing any of those releases creates an orphaned reference. To reduce mistakes, the kernel provides convenience helpers (for example debugfs_lookup_and_remove that perform the grab-and-release (or equivalent) atomically, minimizing the chance of a missed dput. The upstream fix for CVE‑2023‑53410 uses exactly that simplification.

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The upstream fix — what changed in the kernel​

Small, surgical remediation​

Upstream maintainers applied a narrowly scoped change: where the code previously called debugfs_lookup and handled manual cleanup paths, the new code either ensures dput is always invoked on all return paths or replaces the manual pattern with debugfs_lookup_and_remove, which performs the lookup and cleanup in one atomic helper. The patch is intentionally minimal and defensive — a change of this size is standard for lifecycle bugs because it’s low risk and easy to backport to stable kernel trees.

Why that fix is safe and effective​

• It eliminates human error: fewer manual reference-count manipulations reduce the chance of missed releases.
• It keeps public behavior unchanged for correct device interactions while closing the leak only under the error/alternate-control flows.
• The patch is small, straightforward to review, and thus readily included in stable branches by distribution maintainers. This pattern (tiny defensive edits) is common across kernel fixes for robustness and memory-leak classes.

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Who is affected and how serious it is​

Affected code and typical exposure​

• The flaw lives in upstream Linux kernel ULPI code paths and therefore affects kernels that include the ULPI code without the upstream fix.
• Systems that load the ULPI driver or otherwise exercise the driver’s debugfs logic are the primary surface. Many desktop systems, servers, and embedded platforms are only affected if they build or load the ULPI subsystem.

Distributions and vendor status (representative)​

• Debian’s security tracker lists fixed and vulnerable package versions and marks newer stable kernels as containing backports for the fix; older 5.x kernels were initially vulnerable until backports were applied.
• Ubuntu published a CVE entry and gives a medium priority — administrators should consult Ubuntu advisories for package-level mapping.
• Amazon’s ALAS and several commercial scanners list the CVE and the CVSS/EPSS assessments used in enterprise tooling; Amazon reports a CVSS v3 base score of 5.5 (AV:L/AC:L/PR:L/UI:N/C:N/I:N/A:H) in their distribution context.

Realistic attacker model​

• Attack vector: local or local‑adjacent. An attacker must cause the ULPI driver code path to run — for example by attaching or manipulating devices that invoke ULPI interactions or by running local code that triggers the debugfs path.
• Privileges required: typically low — the path may be reachable by processes with limited privileges if the relevant device interfaces and debugfs nodes are accessible.
• Impact: availability (kernel memory growth, performance degradation, eventual OOM conditions), not confidentiality or integrity in most observed analyses. There’s no public evidence the leak by itself leads to privilege escalation or code execution.

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Detection and forensic signals​

What to look for in kernel telemetry​

• Rising kernel slab / kmem usage over time correlated with ULPI or USB attach/detach activity.
• kmemleak reports (if enabled) that show unreferenced allocations with backtraces pointing into ULPI or debugfs lookup code paths.
• Kernel logs (dmesg / journalctl -k) that show repeated debugfs or driver diagnostic messages during device operations; while the leak itself does not always print a clear error, memory pressure warnings and refcount diagnostics are telltale signs.

Repro and test guidance for labs​

1. Reproduce the driver path in a test environment that can exercise ULPI attach/detach and debugfs lookup code paths.
2. Enable kmemleak in the kernel (if possible) and run the repeated trigger loop; inspect kmemleak output for unreferenced allocation traces.
3. Monitor slab occupancy (slabtop, /proc/meminfo) while repeating the trigger to detect growth patterns over time.
4. Validate the fix by booting a patched kernel and repeating the same test; a patched kernel should not show leaking allocations from the same call path.

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Mitigation and remediation playbook​

Immediate (short-term) actions​

• Patch the kernel: install vendor-supplied kernel packages that include the upstream fix and schedule a reboot. Kernel fixes require a reboot to take effect. This is the definitive remediation.
• If you cannot patch immediately, mitigate exposure by restricting access to the relevant device interfaces and debugfs nodes:
  • Tighten file permissions and SELinux/AppArmor policies to prevent untrusted processes from invoking the relevant device operations or ioctls.
  • If the ULPI driver is not needed on a host, consider blacklisting the module or rebuilding the kernel without the ULPI subsystem for that specific environment.
  • For long‑running multi‑tenant hosts, reduce device‑attach capabilities or disable USB passthrough where possible until patched.

Long-term operational hygiene​

• Maintain an inventory of which kernel modules and subsystems are required in production images; remove or disable unused drivers to shrink attack surface and reduce the number of code paths needing urgent patching.
• Run periodic kernel memory health checks (slabtop, kmemleak where safe) and monitor for slow-growing kernel memory usage trends.
• Subscribe to vendor security trackers and map CVE fixes to distribution package versions — vendors often backport the small defensive fixes into supported kernel branches. Debian, Ubuntu, Red Hat, and other vendor trackers already list this CVE in their trackers.

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How to verify whether your systems are patched​

1. Check installed kernel package versions (distribution package manager or uname -r).
2. Consult your distribution security tracker or vendor advisory for the fixed package version mapping (Debian and Ubuntu list package-level status; Amazon Linux and other vendors provide analogous guidance).
3. Inspect kernel changelog and package release notes for references to the upstream stable commit(s) that implement the fix. When vendors report a backport, ensure the package changelog references the upstream commit ID or CVE mapping.
4. After installing the fixed package, reboot into the patched kernel and re-run your test triggers — kmemleak or slab monitoring should no longer show the previous leak trace.

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Broader context — why small reference leaks matter​

A single missed dput is a small bug; however, in long‑uptime infrastructure and multi‑tenant environments, small per‑trigger leaks can add up. Test farms, CI runners, and embedded appliances are precisely the environments where such leaks become operationally visible and costly: automated harnesses repeatedly exercising device paths can turn an otherwise benign leak into a service-disrupting resource exhaustion condition. The Linux kernel project and distribution maintainers therefore treat these fixes seriously even when the immediate exploit risk (RCE/privilege escalation) is low — availability problems in production are real and costly. Parallel incidents across the kernel ecosystem show the same remediation pattern: minimal, defensive changes that close the lifecycle gap and are easy to backport. This conservative strategy reduces regression risk while restoring correct resource-management semantics — a pattern documented in multiple adjacent USB and driver fixes.

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Practical recommendations for Windows administrators who operate mixed estates​

• When Windows hosts run Linux VMs, containers, or WSL images, treat kernel CVEs like CVE‑2023‑53410 seriously when those Linux instances are host to multi‑tenant workloads or are used for device‑test automation. Patch or replace vulnerable kernels in guest images and container base images as part of your image-management pipeline.
• For administrators who manage both Windows and Linux infrastructure, ensure cross-team coordination so Linux kernel updates are included in maintenance windows and vulnerability response processes — kernel reboots are disruptive and need scheduling.
• If USB passthrough from Windows hosts to VMs is allowed, restrict passthrough policies for untrusted tenants until guests are confirmed patched. The attack vector here is local or local‑adjacent — untrusted devices and passthrough paths increase exposure.

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Caveats, limitations, and things we could not verify​

• The upstream kernel commit references are publicly recorded in kernel stable trees; however, direct retrieval of some git.kernel.org commit pages from certain networks may be blocked or return limited content. Vulnerability trackers (NVD, OSV, Debian, Ubuntu) and vendor advisories reproduced the essential fix rationale (replace debugfs_lookup with a variant that enforces cleanup). If you need the raw patch for auditing, fetch the kernel stable commit(s) from kernel.org or mirror sites in your network and cross‑check the commit diff.
• There is no public proof‑of‑concept that demonstrates privilege escalation or remote code execution using this leak alone. Published reports and distribution advisories uniformly classify the impact as availability/resource‑exhaustion rather than confidentiality or integrity compromise. Treat any claims of RCE without corroborating technical evidence as unverified.

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Quick checklist — what to do now​

1. Identify Linux systems that load or compile the ULPI driver (lsmod, kernel config).
2. Map installed kernels to vendor advisories and confirm whether your package versions include the CVE backport.
3. If patched kernels are available: schedule and apply updates; reboot hosts into patched kernels.
4. If immediate patching is impossible: restrict access to device nodes and debugfs, disable USB passthrough where applicable, and consider blacklisting the ULPI module on non‑essential hosts.
5. Monitor kernel slab usage and set alerts for abnormal growth; enable kmemleak in a test environment for definitive confirmation if safe to do so.

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Conclusion​

CVE‑2023‑53410 is a compact but meaningful example of how reference management errors in kernel drivers translate into operational risk. The bug’s root cause — a missed dput after debugfs_lookup — is straightforward to understand and remediate, and upstream maintainers fixed it with a small defensive change (use debugfs_lookup_and_remove or ensure dput on all paths). The security profile is availability‑centric: repeated triggers can leak kernel memory and disrupt long‑running or heavily automated systems, so administrators should treat the CVE as a medium‑priority operational fix: install vendor-supplied kernels that include the upstream backport, or apply mitigating controls until patches can be deployed.

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Source: MSRC Security Update Guide - Microsoft Security Response Center