CVE-2026-5747 is an out-of-bounds write vulnerability (CWE-787) in the virtio PCI transport component of AWS Firecracker, affecting versions 1.13.0 through 1.14.3 and 1.15.0 on x86_64 and aarch64 platforms. The flaw allows a local guest user with root privileges to corrupt memory by modifying virtio queue configuration registers after device activation. This can lead to a denial-of-service condition by crashing the Firecracker VMM process or, under certain conditions involving a custom guest kernel or specific snapshot configurations, enable arbitrary code execution on the host. AWS has acknowledged the issue and released fixed versions. Since Firecracker is a cloud service, AWS manages the remediation process server-side.

The vulnerability can be exploited by a local guest user with root privileges to cause a denial-of-service by crashing the Firecracker VMM process or potentially execute arbitrary code on the host system. Exploitation for code execution requires additional conditions, limiting the ease of exploitation. The CVSS v3.1 base score is 7.5, indicating high severity with high impact on confidentiality, integrity, and availability. There are no known exploits in the wild at this time.

AWS manages remediation for this cloud-hosted service and has released fixed versions of Firecracker to address this vulnerability. Users should ensure they are running the updated Firecracker versions as specified in the AWS security bulletin (https://aws.amazon.com/security/security-bulletins/2026-015-aws/). Patch status is confirmed by the vendor advisory. No additional mitigation actions are required beyond applying the official fix.