CVE-2026-53401: Linux Kernel Use-After-Free Vulnerability

CVE-2026-53401 Overview

CVE-2026-53401 is a use-after-free vulnerability in the Linux kernel's omapfb framebuffer driver. The flaw exists in omapfb_mmap(), which races with the OMAPFB_SETUP_PLANE ioctl handler. The fb_mmap() path acquires mm_lock but not fb_info->lock, while ioctl handlers acquire fb_info->lock but not mm_lock. This locking gap allows an attacker with local access to trigger concurrent execution paths that leave userspace holding a mapping to freed physical memory.

Critical Impact
A local user can obtain a mapping to freed kernel memory regions on affected OMAP2 framebuffer systems, enabling potential memory corruption, privilege escalation, or denial of service.

Affected Products

Linux kernel fbdev subsystem — omap2 framebuffer driver (omapfb)
Systems exposing /dev/fb* devices backed by the OMAP2 driver
Kernel builds prior to the commits 6eb6ebcc8590 and 7958e67375aa

Discovery Timeline

2026-07-19 - CVE-2026-53401 published to NVD
2026-07-20 - Last updated in NVD database

Technical Details for CVE-2026-53401

Vulnerability Analysis

The vulnerability stems from inconsistent locking between the memory-mapping path and the ioctl configuration path in the omapfb driver. The omapfb_mmap() function retrieves a region reference through omapfb_get_mem_region(ofbi->region), then reads start and len values from ofbi and fix->smem_len. These subsequent reads can observe a different region than the one whose map_count is later incremented.

While omapfb_mmap() executes, a concurrent OMAPFB_SETUP_PLANE ioctl can reassign ofbi->region = new_rg and update fix->smem_len. A follow-on OMAPFB_SETUP_MEM ioctl then inspects the new region's map_count, sees zero, and frees it. The userspace caller is left with a valid virtual mapping pointing at physical memory the kernel has reclaimed.

Root Cause

The root cause is a Time-of-Check Time-of-Use (TOCTOU) race condition [CWE-416, CWE-367]. The driver reads mapping parameters from a mutable structure without holding fb_info->lock, so the region reference used for reference counting can diverge from the region whose memory is actually mapped into the process address space.

Attack Vector

An authenticated local attacker with access to the framebuffer device node can exploit this issue. The attacker opens /dev/fb0, issues mmap() calls on one thread, and concurrently issues OMAPFB_SETUP_PLANE and OMAPFB_SETUP_MEM ioctls on another thread. Winning the race yields a userspace mapping to freed physical memory, which can be used to read or corrupt kernel-managed pages after reallocation.

The upstream fix reads start and len from the same region reference rg that receives the atomic_inc(&rg->map_count) call, ensuring the mapped region cannot be freed while a mapping exists.

Detection Methods for CVE-2026-53401

Indicators of Compromise

Unexpected process access patterns against /dev/fb0 or other OMAP2 framebuffer device nodes from non-graphics workloads.
Kernel log entries referencing omapfb, page faults on framebuffer-mapped regions, or KASAN use-after-free reports on omapfb_mem_region structures.
Multi-threaded processes issuing tight loops of mmap() and ioctl() calls with OMAPFB_SETUP_PLANE or OMAPFB_SETUP_MEM commands.

Detection Strategies

Enable KASAN on test kernels to surface use-after-free access on omapfb regions during fuzzing or QA.
Audit auditd and execve telemetry for local processes opening framebuffer devices and issuing framebuffer ioctls without a legitimate display workload.
Correlate kernel oops, general protection fault, or BUG: unable to handle page fault messages with prior framebuffer ioctl activity from the same process.

Monitoring Recommendations

Ship dmesg and /var/log/kern.log to a centralized log store and alert on omapfb, KASAN, or use-after-free strings.
Track running kernel versions across the fleet and flag hosts still on unpatched builds of the omap2 framebuffer driver.
Monitor local privilege escalation indicators such as unexpected uid=0 transitions from processes that previously interacted with /dev/fb*.

How to Mitigate CVE-2026-53401

Immediate Actions Required

Update to a Linux kernel release that includes commits 6eb6ebcc8590007ad59ddccc8b5f9201655b33f8 and 7958e67375aa111522086286bba13cfc0816ce8d.
Restrict access to /dev/fb* device nodes to the video group and remove world-accessible permissions where present.
Inventory embedded and ARM-based systems using the OMAP2 SoC family, since these are the primary platforms exposing omapfb.

Patch Information

The fix is available in the upstream Linux kernel stable tree. Apply the changes referenced in the Kernel Git Commit Note (6eb6ebcc8590) and the Kernel Git Commit Note (7958e67375aa). The patch modifies omapfb_mmap() to read start and len from the same region reference used for map_count accounting, closing the race window.

Workarounds

Disable the omapfb driver in kernel configuration (CONFIG_FB_OMAP2=n) on systems that do not require the OMAP2 framebuffer.
Blacklist the omapfb module and unload it at boot on systems where the framebuffer is not in active use.
Tighten Discretionary Access Control (DAC) on framebuffer device nodes and remove any SUID binaries that expose framebuffer ioctls to unprivileged users.

bash

# Configuration example
# Prevent loading of the omapfb driver on affected systems
echo "blacklist omapfb" | sudo tee /etc/modprobe.d/blacklist-omapfb.conf
sudo depmod -a

# Restrict framebuffer device access to the video group
sudo chown root:video /dev/fb*
sudo chmod 0660 /dev/fb*

# Verify running kernel includes the fix
uname -r