Flipping one bit leaves AMD CPUs open to VM vuln

StackWarp (CVE-2025-29943) is a microarchitectural flaw in AMD Zen CPUs that abuses an undocumented MSR bit to freeze and manipulate the frontend stack engine, enabling a hypervisor-controlled or SMT sibling thread to deterministically alter a SEV‑SNP guest's stack pointer. The researchers demonstrated RSA-2048 private key recovery, OpenSSH and sudo password bypasses, and ring-0 code execution; proof-of-concept code and paper are published and AMD has released patches.