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StackWarp
StackWarp (CVE-2025-29943) is a hardware/microarchitectural vulnerability in AMD Zen 1 through Zen 5 processors that affects confidential virtual machines protected by AMD SEV-SNP. The issue allows an admin-privileged host attacker, such as a malicious hypervisor or compromised cloud host, to modify CPU pipeline configuration in a way that corrupts the stack pointer inside an SEV-SNP guest. Public technical reporting attributes the flaw to improper synchronization in the CPU speculative stack engine and abuse of bit 19 of an undocumented core-scoped MSR (0xC0011029). By toggling this control from a sibling hyperthread, an attacker can freeze and later release stack-pointer updates, injecting a chosen offset into the guest VM’s stack pointer with deterministic precision. This breaks SEV-SNP integrity guarantees without requiring decryption of guest memory and can be used to hijack control flow or data flow inside the protected VM.
What it means and what to do now: patch path, interim mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
Successful exploitation can undermine the integrity of SEV-SNP-protected guests and enable deterministic manipulation of execution state inside a confidential VM. Reported proof-of-concept impacts include authentication bypass in OpenSSH and sudo-related flows, guest privilege escalation including conditions leading the guest to treat a process as root, kernel-mode/ring-0 code execution through kernel stack modification, and extraction of cryptographic secrets such as recovery of an RSA-2048 private key from a faulty signature. More broadly, the vulnerability enables compromise of confidential VMs hosted on affected AMD platforms despite SEV-SNP protections, particularly in hostile-host or multi-tenant cloud threat models.
If you can’t patch tonight, do this now.
As an immediate compensating control, disable Simultaneous Multithreading (SMT) on SEV-SNP hosts, because published research states the attack requires cross-hyperthread manipulation from a sibling logical core. For high-integrity confidential computing deployments, restrict SEV-SNP workloads to fully patched hosts, avoid co-scheduling untrusted host activity on sibling threads, and monitor protected guests for anomalous crashes, stack corruption symptoms, unexpected authentication successes, or unexplained privilege transitions. Detection is inherently difficult because the attack is hardware-based.
Patch, then assume compromise.
Apply AMD-provided microcode and platform/firmware updates referenced in AMD Security Bulletin AMD-SB-3027 for affected Zen 1–5 SEV-SNP-capable processors and associated EPYC/EPYC Embedded product lines. Available reporting indicates AMD released hot-loadable microcode updates for affected products beginning in July 2025 and October 2025, with some AGESA/platform initialization updates for certain EPYC Embedded lines scheduled later. Remediation should include updating host firmware, microcode, and any required platform initialization components across all SEV-SNP hosts.
1 exploit validated by Mallory's analysis.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
13 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.