CVE-2026-97944 x86/cfi: Fix FineIBT hash offset in cfi_get_func_hash()
A kernel bug causes a crash when BPF struct_ops programs are used with FineIBT enabled, requiring local access to trigger.
- 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-2026-97944?
CVE-2026-97944 is a denial of service vulnerability in Linux, published on 25 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/cfi: Fix FineIBT hash offset in cfi_get_func_hash()
The switch of the FineIBT preamble from "subl $hash, %r10d" to the shorter "subl $hash, %eax" moved the hash immediate from offset 7 to offset 5 of the preamble. fineibt_preamble_hash was updated to match, but the open-coded offset in cfi_get_func_hash() was missed and it still reads the hash at offset 7.
cfi_get_func_hash() is used by the BPF JIT to give a struct_ops trampoline the CFI hash of the stub function it stands in for. With FineIBT the trampoline now gets the upper half of the real hash followed by the first two bytes of the next instruction, so the first indirect call from the kernel into a struct_ops program, tcp_init_congestion_control() calling ->init() of a BPF congestion control for example, fails the FineIBT check and the kernel dies with a CFI failure.
Move the FineIBT preamble template and its offset defines above cfi_get_func_hash() and use fineibt_preamble_hash there, so every reader of the preamble shares one definition of its layout. The CFI_FINEIBT arm is only built with CONFIG_FINEIBT, the only configuration in which cfi_mode can take that value. cfi_get_func_arity() does not need the same treatment: the __bhi_args call whose displacement it reads still ends at the function address.
Which versions are affected by CVE-2026-97944?
How do I fix CVE-2026-97944?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-97944 being exploited?
There is no known exploitation of CVE-2026-97944 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-97944, DEBIAN-CVE-2026-97944, GHSA-7jp9-pjx7-g496, UBUNTU-CVE-2026-97944.