# 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.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-102201, BELL-CVE-2026-90359, DEBIAN-CVE-2026-90359, GHSA-h885-6xr2-hvv3, UBUNTU-CVE-2026-90359

## 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.

## Is CVE-2026-90359 being exploited?

There is no known exploitation of CVE-2026-90359 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90359 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-90359 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-90359/ (Markdown: https://insights.sbomify.com/CVE-2026-90359/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90359
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90359
- OSV: https://osv.dev/vulnerability/CVE-2026-90359

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90359/
Summaries are generated and may contain mistakes; the official description above is the record.