CVE-2026-89751 x86/tdx: Fix off-by-one in port I/O handling
An off-by-one error in Linux kernel TDX port I/O handling allows attackers to read or modify unintended memory bits.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89751?
CVE-2026-89751 is a vulnerability in Linux, published on 11 Sep 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:
x86/tdx: Fix off-by-one in port I/O handling
handle_in() and handle_out() in arch/x86/coco/tdx/tdx.c use:
u64 mask = GENMASK(BITS_PER_BYTE * size, 0);
GENMASK(h, l) includes bit h. For size=1 (INB), this produces GENMASK(8, 0) = 0x1FF (9 bits) instead of GENMASK(7, 0) = 0xFF (8 bits). The mask is one bit too wide for all I/O sizes.
Fix the mask calculation.
Which versions are affected by CVE-2026-89751?
How do I fix CVE-2026-89751?
Apply the vendor's patch.
Is CVE-2026-89751 being exploited?
There is no known exploitation of CVE-2026-89751 in the wild and no public exploit code.
Sources
Also known as AZL-100772, BELL-CVE-2026-89751, DEBIAN-CVE-2026-89751, GHSA-pv9x-wp8q-3x5j, UBUNTU-CVE-2026-89751.