CVE-2025-22097 Overview
CVE-2025-22097 is a memory corruption vulnerability in the Linux kernel's Virtual Kernel Mode Setting (vkms) driver. The flaw resides in the driver initialization and cleanup path, where a failure during initialization can lead to both a use-after-free (UAF) and a double-free condition on the default_config pointer. The vulnerability is classified under CWE-416: Use After Free and affects multiple Linux kernel versions. Because the flaw is triggered locally through kernel driver operations, exploitation requires local access with low privileges but can compromise confidentiality, integrity, and availability.
Critical Impact
Local attackers with low privileges may leverage the use-after-free and double-free conditions in the vkms driver to corrupt kernel memory, potentially escalating privileges or causing a denial of service.
Affected Products
- Linux Kernel (multiple stable branches prior to fixed commits)
- Debian LTS distributions shipping vulnerable kernel builds
- Any Linux distribution using the vkms (Virtual Kernel Mode Setting) DRM driver
Discovery Timeline
- 2025-04-16 - CVE-2025-22097 published to NVD
- 2025-05 - Debian LTS advisory released addressing the vulnerability
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-22097
Vulnerability Analysis
The vulnerability exists in the drm/vkms component of the Linux kernel. When the vkms driver initialization routine fails, the corresponding vkms_exit() cleanup function may still be invoked. During cleanup, vkms_exit() accesses the default_config pointer, which at that point may be uninitialized or already freed. This results in two distinct memory safety violations: a use-after-free when the freed pointer is dereferenced, and a double-free when kfree() is called on the same allocation a second time.
Both conditions corrupt the kernel's slab allocator state. A local attacker capable of triggering the failure path during driver initialization can influence the freed memory region through kernel heap grooming techniques. This creates a foundation for kernel memory disclosure or arbitrary write primitives.
Root Cause
The root cause is improper state tracking during initialization. The default_config pointer is assigned before the driver initialization is confirmed successful. When initialization fails partway through, the exit path assumes default_config refers to a valid allocation and both dereferences and frees it. The upstream fix, applied across several stable kernel branches, defers assignment of default_config until initialization has completed successfully.
Attack Vector
Exploitation requires local access to the target system with the ability to load or interact with the vkms driver. The attack vector is local (AV:L) with low complexity and low required privileges. An attacker must be able to trigger the initialization failure path of the vkms driver, which is typically loaded on systems that use virtual displays for testing, headless rendering, or CI environments. Successful exploitation of the resulting UAF or double-free can lead to kernel privilege escalation or system crash.
No public proof-of-concept exploit is currently available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. Refer to the kernel commit history for full patch context.
Detection Methods for CVE-2025-22097
Indicators of Compromise
- Kernel oops or panic messages referencing vkms_exit, default_config, or slab corruption in dmesg output
- KASAN (Kernel Address Sanitizer) reports flagging use-after-free or double-free events in the drm/vkms module
- Unexpected loading or reloading of the vkms kernel module by unprivileged users
Detection Strategies
- Query installed kernel package versions across Linux endpoints and compare against fixed versions listed in vendor advisories
- Monitor kernel ring buffer output for slab allocator warnings, BUG: messages, or general protection faults originating in DRM code
- Enable KASAN in non-production kernels to catch UAF and double-free conditions during test cycles
Monitoring Recommendations
- Ingest kernel logs (/var/log/kern.log, journalctl -k) into a centralized SIEM for correlation of driver-related fault events
- Alert on modprobe or insmod activity targeting the vkms module from non-administrative user contexts
- Track kernel version drift across the Linux fleet to identify hosts pending patch deployment
How to Mitigate CVE-2025-22097
Immediate Actions Required
- Apply the stable kernel updates referenced in the upstream Linux kernel commits as soon as vendor packages are available
- For Debian systems, apply the update described in the Debian LTS Announcement
- Reboot affected systems after patch installation to load the fixed kernel image
Patch Information
The fix has been merged into multiple stable branches of the Linux kernel. The corrective patch defers the assignment of default_config in the vkms driver until initialization has fully succeeded, preventing vkms_exit() from operating on an invalid pointer. Reference commits include 1f68f1cf09d0, 49a69f67f535, 561fc0c5cf41, 79d138d137b8, b8a18bb53e06, d5eb8e347905, and ed15511a773d. Distribution maintainers have backported the fix; consult your vendor's advisory for the exact fixed package version.
Workarounds
- Unload the vkms module (modprobe -r vkms) on systems that do not require virtual display functionality
- Blacklist the vkms module by adding blacklist vkms to /etc/modprobe.d/blacklist-vkms.conf where the driver is unnecessary
- Restrict module loading to privileged users by enabling kernel.modules_disabled=1 after boot on hardened systems
# Configuration example: blacklist the vkms module
echo "blacklist vkms" | sudo tee /etc/modprobe.d/blacklist-vkms.conf
sudo update-initramfs -u
sudo reboot
# Verify the module is not loaded after reboot
lsmod | grep vkms
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
