# CVE-2026-90386: i3c: dw: avoid shift-out-of-bounds when DAA assigns no devices

> A shift-out-of-bounds error in the Linux kernel I3C driver causes a crash when no devices are assigned during boot, leading to denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102134, BELL-CVE-2026-90386, DEBIAN-CVE-2026-90386, GHSA-hx2c-jppg-3c5r, UBUNTU-CVE-2026-90386

## What is CVE-2026-90386?

CVE-2026-90386 is a 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:

i3c: dw: avoid shift-out-of-bounds when DAA assigns no devices

On an empty bus ENTDAA assigns nothing, so cmd->rx_len (the count
of addresses left unassigned) equals master->maxdevs.

The GENMASK() index master->maxdevs - cmd->rx_len - 1 then becomes -1,
which trips up UBSAN. This happens every time on boot on a Gigabyte/AMD
server:

    UBSAN: shift-out-of-bounds in drivers/i3c/master/dw-i3c-master.c:905:12
    shift exponent 64 is too large for 64-bit type 'long unsigned int'
    CPU: 7 UID: 0 PID: 963 Comm: (udev-worker) Not tainted 7.0.11-200.fc44.x86_64 #1 PREEMPT(lazy)
    Hardware name: Giga Computing E163-Z34-AAH1-000/MZ33-DC1-000, BIOS R32_F45 04/01/2026
    Call Trace:
     <TASK>
     dump_stack_lvl+0x5d/0x80
     ubsan_epilogue+0x5/0x2b
     __ubsan_handle_shift_out_of_bounds.cold+0xd7/0x1ab
     dw_i3c_master_daa.cold+0x1b/0x96 [dw_i3c_master]
     i3c_master_do_daa_ext.part.0+0x3e/0xf0 [i3c]

Skip the mask when no new device was assigned.

## Which versions are affected by CVE-2026-90386?


## How do I fix CVE-2026-90386?

Apply the vendor's patch.

## Is CVE-2026-90386 being exploited?

There is no known exploitation of CVE-2026-90386 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90386 and fix it if it is affected.

What it is: CVE-2026-90386 is a 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-2026-90386 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-2026-90386/ (Markdown: https://insights.sbomify.com/CVE-2026-90386/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90386
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90386
- OSV: https://osv.dev/vulnerability/CVE-2026-90386

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90386/
Summaries are generated and may contain mistakes; the official description above is the record.