CVE-2023-52486

What it actually does

Use-after-free in the Linux kernel DRM subsystem caused by failing to reset an fb pointer to NULL after an unref during deadlock handling in drm_mode_page_flip_ioctl, allowing the same framebuffer reference to be released multiple times and freeing an object still in use.

Why it matters to the business

Kernel crashes or hangs in graphics subsystems on Linux systems performing display operations, leading to system instability, loss of graphical sessions, and potential denial of service; high downstream prevalence in Debian and stable kernel trees increases exposure across servers and desktops.

How an attack unfolds

An attacker with local access triggers async page flips under specific mutex contention (such as CONFIG_DEBUG_WW_MUTEX_SLOWPATH) to enter the deadlock retry path, then induces a subsequent error before the next fb lookup to cause repeated unreferencing of the same framebuffer object.

How to fix it

Upgrade linux packages on Debian 12 and 13 to version 6.1.7-1 or later; apply kernel commit 376e21a9e4c2c63ee5d8d3aa74be5082c3882229 or equivalent stable tree patches that reset the fb pointer after unref.

How to confirm the fix worked

Verify the presence of the fb pointer reset logic after the unref in drm_mode_page_flip_ioctl; confirm package versions match the fixed releases and test async flip operations under debug mutex settings to ensure no double-unref occurs.

Typical attack path

1. Obtain local user access on an affected Linux system
2. Invoke DRM page flip ioctls with async flip parameters to induce deadlock conditions
3. Force an error path after the initial fb unref but before the next lookup
4. Trigger repeated unref leading to premature free of an in-use framebuffer
5. Observe resulting kernel oops, busy loops in drm_closefb, or system instability

How to detect it

Review kernel logs for oops messages or busy loops inside drm_closefb and framebuffer list walking; inspect audit or dmesg output for repeated DRM ioctl failures followed by crashes on systems performing async flips.

What your security team should do

• Prioritize kernel upgrades on all systems using DRM graphics within 30 days given publication age and ecosystem reach
• Monitor for kernel oops or framebuffer list busy loops in system logs as immediate indicators
• Restrict unprivileged access to DRM ioctls via SELinux or AppArmor where graphics workloads are not required