CVE-2026-90359 bpf: Reject >8 byte return values on return-reading trampoline paths
A local attacker with high privileges can corrupt memory and leak data by attaching BPF programs to functions returning 16-byte values.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90359?
CVE-2026-90359 is a memory corruption vulnerability in Linux, published on 17 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:
bpf: Reject >8 byte return values on return-reading trampoline paths
btf_distill_func_proto() builds the function model used for the fentry/fexit/fmod_ret/fsession trampolines and struct_ops. It has accepted a 16-byte __int128 return value since the trampoline was introduced: __get_type_size() returns the integer's type size, and the return-type check only rejected ret < 0.
But the BPF trampoline preserves only 8 bytes of the return value (RAX on x86, i.e. R0). For an attach type that reads the target's return value the second half (RDX / R3) is neither saved nor restored, so a program attached to a function returning a 16-byte value corrupts the value seen by the real caller and itself observes only half of it. struct_ops trampolines have the same limitation.
This affects the attach types that read the target's return value: fexit, fmod_ret and fsession (plus the _multi variants of fexit and fsession), and struct_ops. fentry/fentry_multi run before the target returns and are unaffected.
Reject a >8 byte return value for these attach types in bpf_check_attach_target() and bpf_check_attach_btf_id_multi(), and for struct_ops in bpf_struct_ops_desc_init().
Which versions are affected by CVE-2026-90359?
How do I fix CVE-2026-90359?
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-2026-90359 being exploited?
There is no known exploitation of CVE-2026-90359 in the wild and no public exploit code.
Sources
Also known as AZL-102201, BELL-CVE-2026-90359, DEBIAN-CVE-2026-90359, GHSA-h885-6xr2-hvv3, UBUNTU-CVE-2026-90359.