New StackWarp Hardware Flaw Breaks AMD SEV-SNP Protections on Zen 1–5 CPUs

A team of academics from the CISPA Helmholtz Center for Information Security in Germany has disclosed a new hardware vulnerability, codenamed StackWarp, that affects AMD processors and can allow privileged attackers to run malicious code inside confidential virtual machines, undermining AMD Secure Encrypted Virtualization with Secure Nested Paging (SEV-SNP) protections on Zen 1 through Zen 5 CPUs.

The flaw enables a malicious VM host to manipulate the guest VM’s stack pointer, potentially enabling remote code execution and privilege escalation within a confidential VM, according to the researchers Ruiyi Zhang, Tristan Hornetz, Daniel Weber, Fabian Thomas and Michael Schwarz.

AMD is tracking the vulnerability as CVE-2025-29943 (CVSS v4 score: 4.6) and describes it as a medium-severity improper access control bug that could let an admin-privileged attacker alter CPU pipeline configuration and corrupt the stack pointer inside an SEV-SNP guest. The issue affects AMD EPYC 7003, 8004, 9004 and 9005 series processors, including embedded variants, and the researchers note that it exploits a previously undocumented hypervisor control bit and a stack engine microarchitectural optimisation.

Microcode updates were released in July and October 2025, with AGESA patches for certain embedded series scheduled for release in April 2026.