CVE-2026-31578: Linux Kernel Use-After-Free Vulnerability

CVE-2026-31578 Overview

CVE-2026-31578 is a use-after-free and double-free vulnerability [CWE-416] in the Linux kernel's as102 USB media driver. The flaw exists in the as102_usb_probe() function, where a race condition between device registration cleanup and an in-flight open() from userspace allows the as102_dev_t structure to be freed while a valid file descriptor still references it. When the file descriptor is later closed, as102_release() invokes as102_usb_release() on the already-freed memory, triggering both use-after-free and double-free conditions.

Critical Impact
A local attacker racing open() against driver error-path cleanup can corrupt kernel heap memory, potentially leading to local privilege escalation or kernel crash.

Affected Products

Linux Kernel (multiple stable branches prior to fixes in commits 09e9206, 2eeae47, 582fbec, 7e5aedf, 8bd29db, and cb80920)
Systems shipping the as102 DVB-T USB media driver
Distributions using vulnerable upstream kernel revisions

Discovery Timeline

2026-04-24 - CVE-2026-31578 published to NVD
2026-04-27 - Last updated in NVD database

Technical Details for CVE-2026-31578

Vulnerability Analysis

The as102 USB driver allocates an as102_dev_t structure with kzalloc() during probe and then registers a character device via usb_register_dev(). Once registration succeeds, userspace can immediately open() the resulting device node. File descriptors obtained this way remain valid until their final reference is dropped, even if the device is subsequently unregistered.

If an error occurs later in as102_usb_probe(), the driver calls usb_deregister_dev() and then immediately invokes kfree() on the as102_dev_t allocation. A userspace process that won the race and already holds an open file descriptor will eventually close it, invoking as102_release() which calls as102_usb_release() and frees the structure again. The first access in the release path dereferences freed memory, and the subsequent kfree() constitutes a double-free.

Root Cause

The root cause is incorrect ownership of the device structure after usb_register_dev() succeeds. The driver assumed it could synchronously free the allocation on its error path, ignoring that outstanding file descriptors still hold references through the character device subsystem. Lifetime management must be transferred to the .release() callback once registration completes.

Attack Vector

Exploitation requires local access on a system with the as102 USB driver loaded and an attached or simulated as102 device that triggers an error path in as102_usb_probe(). An attacker repeatedly invokes open() on the device node while probe cleanup runs, attempting to win the race window between usb_register_dev() succeeding and the subsequent kfree(). A successful race yields a dangling file descriptor that, when closed, frees attacker-influenced kernel heap memory a second time. With heap grooming, this primitive can be escalated to arbitrary kernel write and privilege escalation.

No public proof-of-concept exploit is currently available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-31578

Indicators of Compromise

Kernel oops or panic messages referencing as102_release, as102_usb_release, or kfree in the call trace
KASAN reports flagging use-after-free or double-free in the as102 module
Unexpected as102 driver crashes correlated with USB hotplug events or repeated open() attempts on /dev/as102_* nodes

Detection Strategies

Enable Kernel Address Sanitizer (KASAN) in test and pre-production kernels to surface UAF and double-free events in the as102 code path
Monitor kernel ring buffer output (dmesg, journalctl -k) for BUG: KASAN, general protection fault, or slab-use-after-free entries tied to the as102 module
Audit running kernels with uname -r and package inventories against the patched commit hashes referenced in the vendor advisories

Monitoring Recommendations

Forward kernel logs to a centralized log platform and alert on crash signatures referencing media or USB driver modules
Track loaded kernel modules across the fleet and flag hosts still loading the unpatched as102 driver
Watch for unusual local process activity that repeatedly opens DVB device nodes, which may indicate race exploitation attempts

How to Mitigate CVE-2026-31578

Immediate Actions Required

Apply the upstream Linux kernel patches referenced in the Kernel Commit 09e9206, Kernel Commit 2eeae47, and related stable backports
Update to a distribution kernel that includes the fix and reboot affected hosts
If patching is not immediately feasible, blacklist the as102 module on systems that do not require DVB-T functionality

Patch Information

The upstream fix removes the direct kfree(as102_dev_t) call from the as102_usb_probe() error path once usb_register_dev() has succeeded. Instead, freeing is deferred to the driver's .release() callback, ensuring the structure persists until the last outstanding file descriptor is closed. Stable backports are available in commits 582fbec, 7e5aedf, 8bd29db, and cb80920.

Workarounds

Blacklist the as102 kernel module by adding blacklist as102 to a file under /etc/modprobe.d/ and regenerating the initramfs
Restrict physical USB access on affected hosts to prevent attachment of as102-compatible DVB-T devices
Tighten permissions on /dev/as102_* device nodes so only trusted users can open them

bash

# Configuration example
# Disable the vulnerable driver until patched kernels are deployed
echo 'blacklist as102' | sudo tee /etc/modprobe.d/disable-as102.conf
sudo rmmod as102 2>/dev/null || true
sudo update-initramfs -u

# Verify the module is no longer loaded
lsmod | grep as102 || echo "as102 not loaded"