AMD SEV firmware - ASK validation in SEND_START: Insufficient validation of the AMD SEV Signing Key in the SEND_START

Impact

Insufficient validation of the AMD SEV Signing Key in the SEND_START command lets a locally authenticated attacker wedge the PSP. SEND_START is part of the guest migration/export flow, so a tenant-triggered migration path can take the secure processor out - and with the PSP down, every confidential guest on the node loses its attestation and key services.

Who can reach it

Local, authenticated. Exercised through the SEV guest export path.

What to do

Fixed in AMD reference firmware (AGESA / PSP / SEV firmware) and delivered only as an OEM SBIOS/BIOS package - Dell, HPE, Supermicro, Lenovo and the ODMs each rebuild and requalify AMD's AGESA drop before shipping. **Expect one to six months of OEM lag**, and on end-of-support platforms expect nothing. Applying it is a drain plus full power cycle, not a driver reload. Verify by reading back the PSP/SMU firmware version afterwards rather than trusting the BIOS version string. This sits inside the SEV-SNP trust boundary, so the update moves the platform's reported TCB version: refresh VCEK certificates from AMD's KDS and update any attestation policy your tenants pin, or confidential guest launches will start failing right after the BIOS lands.

References