CVE-2025-40304 fbdev: Add bounds checking in bit_putcs to fix vmalloc-out-of-bounds
A missing bounds check in the Linux kernel framebuffer driver allows out-of-bounds writes, potentially causing crashes or code execution.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40304?
CVE-2025-40304 is a high-severity memory corruption vulnerability in Linux, published on 8 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
fbdev: Add bounds checking in bit_putcs to fix vmalloc-out-of-bounds
Add bounds checking to prevent writes past framebuffer boundaries when rendering text near screen edges. Return early if the Y position is off-screen and clip image height to screen boundary. Break from the rendering loop if the X position is off-screen. When clipping image width to fit the screen, update the character count to match the clipped width to prevent buffer size mismatches.
Without the character count update, bit_putcs_aligned and bit_putcs_unaligned receive mismatched parameters where the buffer is allocated for the clipped width but cnt reflects the original larger count, causing out-of-bounds writes.
Which versions are affected by CVE-2025-40304?
How do I fix CVE-2025-40304?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2025-40304 being exploited?
There is no known exploitation of CVE-2025-40304 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40304, DEBIAN-CVE-2025-40304, GHSA-6cgq-9674-3xfg, ROOT-OS-DEBIAN-12-CVE-2025-40304, ROOT-OS-DEBIAN-13-CVE-2025-40304, ROOT-OS-UBUNTU-2204-CVE-2025-40304 and 2 more.