CVE-2026-31760 Overview
CVE-2026-31760 is a memory leak vulnerability in the Linux kernel's gpib subsystem, specifically within the lpvo_usb driver. The driver iterates over registered USB interfaces during General Purpose Interface Bus (GPIB) attach operations and acquires references to their USB devices until a match is found. These references are never released, producing a kernel memory leak when devices are disconnected. Repeated attach and disconnect cycles can exhaust kernel memory resources over time. The Linux kernel maintainers have committed fixes that drop the unnecessary references.
Critical Impact
Repeated USB device attach and disconnect operations leak kernel memory references in the lpvo_usb GPIB driver, potentially leading to resource exhaustion on long-running systems.
Affected Products
- Linux kernel versions containing the gpib: lpvo_usb driver prior to the fix commits
- Systems using GPIB over USB hardware with the lpvo_usb driver loaded
- Distributions shipping vulnerable Linux kernel builds before patches are backported
Discovery Timeline
- 2026-05-01 - CVE-2026-31760 published to NVD
- 2026-05-01 - Last updated in NVD database
Technical Details for CVE-2026-31760
Vulnerability Analysis
The vulnerability is classified as a Memory Leak [CWE-401] in the Linux kernel's gpib subsystem. The lpvo_usb driver implements GPIB protocol support over USB-attached hardware. During the GPIB attach routine, the driver walks the list of registered USB interfaces to locate the device matching the requested instance.
While iterating, the driver calls reference-acquiring helpers on candidate USB devices. These reference counts are not decremented for non-matching candidates, nor for the matched device on subsequent paths. The leaked references prevent the kernel from fully releasing the associated struct usb_device allocations on disconnect.
Over repeated attach and disconnect cycles, the leaked references accumulate. On long-running hosts that hot-plug GPIB-USB hardware, this consumes kernel memory and pins device structures that should be freed.
Root Cause
The root cause is missing reference release calls in the USB interface iteration loop within the lpvo_usb GPIB driver. The driver acquires usb_device references via the standard kernel reference helpers but does not pair each acquisition with a corresponding put on the non-matching path. The fix drops the unnecessary reference acquisitions and ensures balanced reference counting.
Attack Vector
The attack vector requires local hardware interaction with GPIB-USB devices on a system that loads the lpvo_usb driver. Triggering the leak requires the ability to attach and disconnect USB GPIB hardware. The vulnerability is a reliability and resource exhaustion issue rather than a remote exploitation primitive. No public proof-of-concept exploit is available, and the issue is not listed in the CISA Known Exploited Vulnerabilities catalog.
No verified exploitation code is available for this vulnerability. Refer to the upstream commits referenced in the NVD entry for the precise patch diff and affected functions.
Detection Methods for CVE-2026-31760
Indicators of Compromise
- Steadily increasing kernel slab allocations associated with usb_device objects on systems that repeatedly attach and disconnect GPIB-USB hardware
- kmemleak reports referencing allocations originating from the lpvo_usb GPIB attach path
- Persistent struct usb_device entries in /sys/kernel/debug/usb that remain after physical device disconnect
Detection Strategies
- Enable CONFIG_DEBUG_KMEMLEAK on test kernels and inspect /sys/kernel/debug/kmemleak after exercising GPIB attach and disconnect cycles
- Audit kernel package versions across managed Linux fleets and compare against the fixed commit hashes 21f942879f86, 5cefb52c1af6, and 706f4fe2dacc
- Monitor /proc/meminfoSlab and SUnreclaim trends on systems running the lpvo_usb module
Monitoring Recommendations
- Track loaded kernel modules and flag hosts where lpvo_usb is present but the kernel build predates the fix commits
- Alert on uptime-correlated growth of kernel memory consumption on hosts handling GPIB-USB hardware
- Centralize kernel logs to capture USB enumeration and disconnect events for correlation with memory pressure indicators
How to Mitigate CVE-2026-31760
Immediate Actions Required
- Identify Linux hosts that load the lpvo_usb GPIB driver using lsmod | grep lpvo_usb and inventory their kernel versions
- Apply vendor-supplied kernel updates that incorporate the upstream fix commits referenced in the NVD entry
- Schedule reboots after patching to unload the vulnerable module and reclaim leaked kernel memory
Patch Information
The fix is available in the upstream Linux kernel through three stable commits: 21f942879f86, 5cefb52c1af6, and 706f4fe2dacc. Each commit removes the unnecessary usb_device reference acquisitions in the lpvo_usb GPIB attach path. Distribution maintainers backport these commits into their stable kernel branches; consult your distribution's security advisories for the corresponding package versions.
Workarounds
- Unload the lpvo_usb module with modprobe -r lpvo_usb on systems that do not require GPIB-USB functionality
- Blacklist the lpvo_usb module in /etc/modprobe.d/ to prevent automatic load on systems without GPIB hardware
- Periodically reboot systems that must use the unpatched driver to reclaim leaked kernel memory
# Blacklist the vulnerable module on systems without GPIB-USB hardware
echo "blacklist lpvo_usb" | sudo tee /etc/modprobe.d/blacklist-lpvo_usb.conf
sudo modprobe -r lpvo_usb
sudo update-initramfs -u
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
