# CVE-2026-13216: Out-of-bounds stack write in Zephyr virtio PCI driver from unvalidated device-supplied capability length

> A malicious virtio device can trigger an out-of-bounds stack write in the Zephyr kernel during boot, potentially leading to code execution or crashes.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/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:** No
- **Published:** 25 Aug 2026
- **Updated:** 25 Aug 2026
- **Also known as:** GHSA-qrh3-4mvv-w667

## What is CVE-2026-13216?

CVE-2026-13216 is a medium-severity memory corruption vulnerability in zephyrproject zephyr, published on 25 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

The virtio PCI driver (drivers/virtio/virtio_pci.c) parses a device's PCI capability list during driver initialization. In virtio_pci_read_cap() the device-supplied capability length byte cap_len (read from PCI config space via pcie_conf_read()) was only checked with assert(tmp.cap_len == cap_struct_size). That assert resolves to __ASSERT_NO_MSG(), gated by CONFIG_ASSERT, which defaults off in production builds, so the value reached the copy logic completely unvalidated.

The length then drives a loop that copies extra capability dwords into a fixed-size stack buffer supplied by the caller. A cap_len below the 24-byte base struct virtio_pci_cap underflows the unsigned extra_data_words count to a near-SIZE_MAX value, producing an effectively unbounded stack write; a cap_len above the caller's buffer (up to 255) writes up to roughly 228 bytes of device-controlled data past the buffer. Both are out-of-bounds writes of attacker-controlled content executed in kernel mode during boot-time device probe.

The input originates from the virtio device. In the common deployment where Zephyr runs as a guest under a hypervisor, the device backend is the host, which already fully outranks the guest, so the bug yields no privilege escalation. The exploitable case is a virtio device that is untrusted relative to the Zephyr kernel — an untrusted or physical/passthrough virtio PCIe device on a bare-metal system, or a confidential-computing posture where the guest must defend against the host — where a malicious device can corrupt the kernel stack and potentially achieve code execution or a crash.

The fix replaces the compiled-out assert with a runtime range check rejecting cap_len outside [sizeof(struct virtio_pci_cap), cap_struct_size] before any arithmetic or copy.

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

## Which versions are affected by CVE-2026-13216?


## How do I fix CVE-2026-13216?

No fix has been published for CVE-2026-13216 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-13216 being exploited?

There is no known exploitation of CVE-2026-13216 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-13216 and fix it if it is affected.

What it is: CVE-2026-13216 is a medium-severity memory corruption vulnerability in zephyrproject zephyr, published on 25 Aug 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-2026-13216 in the wild and no public exploit code.

Affected product: zephyrproject zephyr. 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-2026-13216/ (Markdown: https://insights.sbomify.com/CVE-2026-13216/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-13216
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-13216
- OSV: https://osv.dev/vulnerability/CVE-2026-13216

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-13216/
Summaries are generated and may contain mistakes; the official description above is the record.