CVE-2026-80578 fbdev: core: Fix pointer desynchronization in fb_io_read()
A pointer desynchronization bug in the Linux kernel's fbdev core allows out-of-bounds hardware reads, potentially leading to information disclosure or system crashes.
- 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-2026-80578?
CVE-2026-80578 is a high-severity memory corruption vulnerability in Linux, published on 26 Aug 2026. 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: core: Fix pointer desynchronization in fb_io_read()
In fb_io_read(), if copy_to_user() performs a partial copy (e.g., due to a faulty user buffer), the loop adjusts the chunk size 'c' and updates the remaining 'count'. However, the hardware 'src' pointer has already been eagerly advanced by the original chunk size.
If the loop is allowed to continue, the read will resume from an incorrect, over-advanced offset. Since the remaining 'count' was only decremented by the successful bytes, this desynchronization causes the next iterations to execute more hardware reads than originally bounded, eventually leading to out-of-bounds I/O reads.
Fix this by breaking out of the loop immediately upon a partial copy_to_user(). A partial copy indicates a faulty user buffer, making subsequent read attempts futile. Breaking out ensures we return the number of successfully read bytes without risking out-of-bounds hardware accesses in subsequent mismatched iterations.
Which versions are affected by CVE-2026-80578?
How do I fix CVE-2026-80578?
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-2026-80578 being exploited?
There is no known exploitation of CVE-2026-80578 in the wild and no public exploit code.
Sources
Also known as AZL-97719, BELL-CVE-2026-80578, DEBIAN-CVE-2026-80578, GHSA-fvfx-mw36-f75m, UBUNTU-CVE-2026-80578.