CVE-2025-62626: 
Echo vulnerability analysis and mitigation

The vulnerability CVE-2025-62626 affects AMD's "Zen 5" processors, involving a bug in the RDSEED instruction that may return 0 at a rate inconsistent with randomness while incorrectly signaling success. The issue was initially reported through the Linux kernel mailing list and affects the 16-bit and 32-bit forms of the RDSEED instruction, while the 64-bit form remains unaffected. The vulnerability was assigned a CVSS score of 7.2 (High) (AMD Security Bulletin).

The vulnerability stems from improper handling of insufficient entropy in AMD CPUs, specifically affecting the RDSEED instruction implementation. When the instruction returns a value of 0, it incorrectly sets the carry flag (CF=1) to indicate success, leading to a potential misclassification of failure as success. This issue specifically impacts the 16-bit and 32-bit forms of the RDSEED instruction on Zen 5 processors, while the 64-bit form remains unaffected (AMD Security Bulletin).

The vulnerability could allow a local attacker to influence the values returned by the RDSEED instruction, potentially resulting in the consumption of insufficiently random values. This poses risks to cryptographic operations and security functions that rely on hardware-generated random numbers, potentially compromising both confidentiality and integrity of affected systems (AMD Security Bulletin).

AMD has announced several temporary workaround options while awaiting the final microcode patch: 1) Use the 64-bit form of RDSEED, 2) Mask the CPUID Fn00000007EBX[18] RDSEED from software discovery, 3) Treat RDSEED returning 0 as equivalent to CF=0, and 4) Retry RDSEED later until a non-zero value is returned with CF=1. Permanent fixes are planned for release through microcode updates, with target release dates varying by processor family. For EPYC 9005 Series Processors, the microcode mitigation (Turin C1: 0x0B00215A, Turin Dense B0: 0x0B101054) was released on 2025-10-28, while other processor families are scheduled for updates in late November 2025 (AMD Security Bulletin).