ESCAPING FIRECRACKER FROM GUEST USERSPACE

Summary from the TLDR InfoSec newsletter

Coinspect demonstrated a Firecracker sandbox escape from guest userspace. CVE-2026-122192 allowed a guest to read and modify live Firecracker VMM memory and gain code execution in the host-side process. The flaw stemmed from a failed memory replacement after a snapshot-backed RAM discard, leaving a stale KVM memory slot pointing to reused VMM memory. A second issue, FC-03, allowed VMM code to use io_uring to perform host operations blocked by seccomp, including sending a network message to a host listener. Firecracker v0.23.0 through v1.16.1 are affected. v1.16.2 and v1.17.0 fix the escape.