StackWarp is a hardware vulnerability disclosed by researchers at CISPA Helmholtz Center for Information Security that affects AMD processors from Zen 1 through Zen 5 architectures implementing SEV-SNP technology. SEV-SNP is designed to protect confidential virtual machines by encrypting their memory and isolating them from the hypervisor. However, StackWarp exploits a microarchitectural feature known as the stack engine, which accelerates stack operations, by manipulating a previously undocumented control bit accessible to the hypervisor. This manipulation allows an attacker with administrative privileges on the host to corrupt the stack pointer inside a protected VM. By controlling the stack pointer, the attacker can hijack both control flow and data flow within the VM, enabling remote code execution and privilege escalation. This attack does not require reading the VM's plaintext memory, thus bypassing SEV-SNP's encryption protections. The vulnerability affects multiple AMD EPYC product lines including the 7003, 8004, 9004, and 9005 series, both standard and embedded variants. Exploitation can lead to exposure of cryptographic secrets such as RSA-2048 private keys from a single faulty signature, effectively bypassing OpenSSH password authentication and sudo password prompts, and achieving kernel-mode code execution inside the VM. AMD has released microcode updates in mid and late 2025, with further AGESA patches scheduled for April 2026. Researchers recommend disabling hyperthreading on affected hosts as a temporary mitigation, especially for VMs with high integrity requirements. StackWarp builds upon prior research such as CacheWarp, highlighting how subtle microarchitectural optimizations can undermine hardware-based security guarantees in confidential computing environments.

For European organizations, the StackWarp vulnerability poses a significant risk to the confidentiality and integrity of workloads running on AMD EPYC-based servers, particularly those leveraging SEV-SNP for confidential computing. Many European cloud providers and enterprises utilize AMD EPYC processors for their server infrastructure due to their performance and security features. Successful exploitation could allow attackers with host-level privileges—such as malicious insiders, compromised administrators, or attackers who have gained hypervisor access—to execute arbitrary code within protected VMs, escalate privileges, and extract sensitive cryptographic keys. This undermines trust in confidential computing deployments, potentially exposing intellectual property, personal data, and critical business secrets. The ability to bypass authentication mechanisms like OpenSSH and sudo further increases the risk of lateral movement and persistent compromise. Although exploitation requires privileged access and is not trivial, the widespread deployment of affected AMD EPYC processors in European data centers and cloud environments amplifies the threat surface. The vulnerability could also impact government, financial, healthcare, and critical infrastructure sectors that rely on confidential VMs for sensitive workloads. Without timely mitigation, organizations face risks of data breaches, regulatory non-compliance, and operational disruptions.

European organizations should take the following specific mitigation steps: 1) Immediately inventory all AMD EPYC processors in use, focusing on affected series (7003, 8004, 9004, 9005, and embedded variants) running SEV-SNP-enabled confidential VMs. 2) Assess whether hyperthreading is enabled on these hosts; if so, plan to disable hyperthreading temporarily for VMs with high integrity or confidentiality requirements to reduce attack surface. 3) Apply all available microcode and firmware updates released by AMD, including the July and October 2025 microcode patches and upcoming AGESA updates scheduled for April 2026. 4) Coordinate with cloud service providers to confirm patch status and mitigation measures if using third-party infrastructure. 5) Monitor hypervisor and host logs for unusual activity that could indicate attempts to manipulate the stack pointer or exploit the vulnerability. 6) Implement strict access controls and monitoring for administrative privileges on host systems to prevent unauthorized hypervisor-level access. 7) Consider additional isolation strategies such as dedicated hardware or separate physical hosts for highly sensitive confidential workloads. 8) Stay informed on further research or patches related to StackWarp and related microarchitectural attacks to adapt defenses accordingly.