CVE-2026-64245: Linux Kernel Use-After-Free Vulnerability

CVE-2026-64245 Overview

CVE-2026-64245 is a use-after-free vulnerability in the Linux kernel's framebuffer device (fbdev) subsystem. The flaw resides in the fb_find_mode() function within drivers/video/fbdev/core/modedb.c. When the mode_option parameter is NULL, the function allocates a buffer via fb_get_options() and assigns it to mode_option. A local name pointer then aliases this buffer, but mode_option_buf is freed with kfree() while name is still dereferenced during subsequent mode matching. The kernel maintainers resolved the issue by extending the buffer's lifetime through scope-based resource management.

Critical Impact
Access to freed heap memory in the fbdev modedb path can lead to memory corruption or information disclosure in kernel space when the framebuffer subsystem parses mode options.

Affected Products

Linux kernel (fbdev subsystem, drivers/video/fbdev/core/modedb.c)
Distributions shipping affected stable kernel branches referenced in the upstream fix commits
Systems relying on fbdev-based display initialization

Discovery Timeline

2026-07-24 - CVE-2026-64245 published to NVD
2026-07-30 - Last updated in NVD database

Technical Details for CVE-2026-64245

Vulnerability Analysis

The defect is a classic use-after-free [CWE-416] in the fbdev mode database resolver. The fb_find_mode() function accepts an optional mode_option string describing the requested video mode. When the caller passes NULL, the function invokes fb_get_options(NULL, &mode_option_buf) to retrieve a default option string and assigns mode_option = mode_option_buf.

A subsequent const char *name = mode_option; creates an alias to the heap buffer. The function later calls kfree(mode_option_buf) before the name pointer's last use inside the mode-matching loop, which invokes name_matches(db[i], name, namelen). Because name still references the freed allocation, the comparison reads memory that may have been reallocated or scrubbed.

Root Cause

The root cause is incorrect object-lifetime management. The freed buffer and the pointer used for string comparison share the same backing memory, but the free occurs before the last read. The upstream fix replaces manual kfree() with scope-based cleanup, ensuring mode_option_buf remains valid until fb_find_mode() returns.

Attack Vector

Exploitation requires local execution paths that trigger fb_find_mode() with a NULLmode_option, typically during framebuffer driver initialization or reconfiguration. An attacker capable of influencing heap layout between the kfree() and the subsequent read could stage a use-after-free primitive. The specific attack surface depends on which drivers invoke fb_find_mode() and whether unprivileged callers can reach it.

No verified public exploit code is available. Refer to the upstream commits for the exact patch semantics: Linux Kernel Commit 13b6f0c, Linux Kernel Commit 4d418cf, Linux Kernel Commit 85b6256, Linux Kernel Commit c7dc382, and Linux Kernel Commit f906347.

Detection Methods for CVE-2026-64245

Indicators of Compromise

Unexpected kernel oops, GPF, or KASAN use-after-free reports referencing fb_find_mode or name_matches in the call stack.
Kernel log entries from the fbdev subsystem coinciding with framebuffer driver load or mode change events.
Systems running kernels predating the referenced stable commits without vendor backports applied.

Detection Strategies

Enable KASAN (Kernel Address Sanitizer) on test builds to surface use-after-free reads inside fb_find_mode().
Inventory installed kernel versions against the fixed commits listed in the NVD references and flag hosts missing the backport.
Monitor dmesg and journald for framebuffer-related kernel warnings tied to mode option parsing.

Monitoring Recommendations

Forward kernel logs to a centralized logging platform and alert on repeated fbdev-related crashes.
Track kernel package versions across the fleet to identify unpatched systems.
Correlate framebuffer driver initialization events with subsequent kernel instability.

How to Mitigate CVE-2026-64245

Immediate Actions Required

Apply the upstream kernel patches referenced in the NVD advisory for all affected stable branches.
Update to distribution-provided kernel packages that include the fbdev modedb fix.
Reboot systems after patching to ensure the corrected kernel is active.

Patch Information

The fix extends the lifetime of mode_option_buf until the end of fb_find_mode() using scope-based resource management, eliminating the alias between the freed buffer and the name pointer. Verified fix commits are available at Linux Kernel Commit 13b6f0c, Linux Kernel Commit 4d418cf, Linux Kernel Commit 85b6256, Linux Kernel Commit c7dc382, and Linux Kernel Commit f906347.

Workarounds

On systems that do not require legacy fbdev, disable the framebuffer subsystem or blacklist unnecessary fbdev drivers via kernel module configuration.
Restrict local access on multi-user systems to reduce exposure until patches are deployed.
Prefer KMS/DRM-based display stacks where the affected fbdev code path is not exercised.

bash

# Verify installed kernel version and confirm patch presence
uname -r
grep -R "fb_find_mode" /usr/src/linux-$(uname -r)/drivers/video/fbdev/core/modedb.c | head

# Example: blacklist an unused fbdev driver until patched (Debian/Ubuntu)
echo "blacklist vesafb" | sudo tee /etc/modprobe.d/blacklist-fbdev.conf
sudo update-initramfs -u