Executive brief
Firecracker is a virtualization technology used to run secure, isolated containers and serverless functions. A vulnerability in its PCI transport component could allow a user with administrative access inside a virtual machine to crash the hosting service or potentially execute code on the underlying host server. While difficult to exploit, this could lead to a total compromise of the host and any other virtual machines running on it.
Technical details
An out-of-bounds write vulnerability exists in the virtio PCI transport of Firecracker due to improper enforcement of the virtio device initialization sequence. A local guest user with root privileges can modify the 'queue_size' configuration register after device activation, bypassing the bounds validation performed during initial setup. This can lead to a divide-by-zero error causing a VMM crash (DoS) or an out-of-bounds write of up to 524,284 bytes. While standard Linux kernels typically restrict this write to guest memory, specific conditions—such as custom guest kernels or unique snapshot configurations—can enable an attacker to write into the host's memory space. The issue is addressed in versions 1.14.4 and 1.15.1; users can mitigate the risk by disabling the opt-in PCI transport and using the default MMIO transport.
Affected products
- Amazon Firecracker 1.13.0 through 1.14.3, 1.15.0
Timeline
- 2026-04-07: patched: Fixed in versions 1.14.4 and 1.15.1
- 2026-04-08: disclosed: Initial public advisory published