New StackWarp Attack Threatens Confidential VMs on AMD Processors

SecurityWeek reports a new hardware vulnerability, named StackWarp, that affects AMD Zen 1 through Zen 5 processors and can enable remote code execution inside confidential VMs. The researchers describe StackWarp as a software-based architectural attack that exploits a synchronization failure in the stack engine, allowing a malicious VM host to hijack a guest VM’s stack pointer and break isolation.

In practical demonstrations, they reconstructed an RSA-2048 private key, bypassed OpenSSH password authentication, and achieved kernel‑mode code execution within a CVM. Attacks of this kind typically require privileged control over the host server, and claims suggest rogue employees of a cloud provider or a sophisticated threat actor could initiate them.

According to AMD, a security advisory has been published, the flaw has a low severity rating, and patches have been available for the impacted EPYC server products since July 2025; the CVE identifier is CVE-2025-29943, and the researchers have set up a dedicated StackWarp site and a Usenix26 paper with full technical details.