# CVE-2026-46123: Bluetooth: virtio_bt: clamp rx length before skb_put

> A malicious Bluetooth backend can trigger uninitialized memory disclosure or denial of service in the Linux kernel by sending invalid packet lengths.

- **Severity:** High 7.7 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H`)
- **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:** 28 May 2026
- **Updated:** 5 Aug 2026
- **Also known as:** AZL-89096, BELL-CVE-2026-46123, DEBIAN-CVE-2026-46123, GHSA-qxc2-9rg4-2rgv, ROOT-OS-DEBIAN-12-CVE-2026-46123, ROOT-OS-UBUNTU-2204-CVE-2026-46123, ROOT-OS-UBUNTU-2404-CVE-2026-46123, UBUNTU-CVE-2026-46123

## What is CVE-2026-46123?

CVE-2026-46123 is a high-severity memory corruption vulnerability in Linux kernel, published on 28 May 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:

Bluetooth: virtio_bt: clamp rx length before skb_put

virtbt_rx_work() calls skb_put(skb, len) where len comes directly
from virtqueue_get_buf() with no validation against the buffer we
posted to the device. The RX skb is allocated in virtbt_add_inbuf()
and exposed to virtio as exactly 1000 bytes via sg_init_one().

Checking len against skb_tailroom(skb) is not sufficient because
alloc_skb() can leave more tailroom than the 1000 bytes actually
handed to the device. A malicious or buggy backend can therefore
report used.len between 1001 and skb_tailroom(skb), causing skb_put()
to include uninitialized kernel heap bytes that were never written by
the device.

The same path also accepts len == 0, in which case skb_put(skb, 0)
leaves the skb empty but virtbt_rx_handle() still reads the pkt_type
byte from skb->data, consuming uninitialized memory.

Define VIRTBT_RX_BUF_SIZE once and reuse it in alloc_skb() and
sg_init_one(), and gate virtbt_rx_work() on that same constant so
the bound checked matches the buffer actually exposed to the device.
Reject used.len == 0 in the same gate so an empty completion can
no longer reach virtbt_rx_handle().

Use bt_dev_err_ratelimited() because the length value comes from an
untrusted backend that can otherwise flood the kernel log.

Same class of bug as commit c04db81cd028 ("net/9p: Fix buffer
overflow in USB transport layer"), which hardened the USB 9p
transport against unchecked device-reported length.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-46123?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-46123?

Apply the vendor's patch.

## Is CVE-2026-46123 being exploited?

There is no known exploitation of CVE-2026-46123 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-46123 and fix it if it is affected.

What it is: CVE-2026-46123 is a high-severity memory corruption vulnerability in Linux kernel, published on 28 May 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-2026-46123 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-46123/ (Markdown: https://insights.sbomify.com/CVE-2026-46123/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-46123
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-46123
- OSV: https://osv.dev/vulnerability/CVE-2026-46123

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-46123/
Summaries are generated and may contain mistakes; the official description above is the record.