AMD has disclosed a vulnerability affecting the random number generation capabilities of its Zen 5 processors.
The issue, tracked as CVE-2025-62626 and identified by AMD as AMD-SB-7055, impacts the RDSEED instruction, a critical component responsible for generating cryptographic random numbers.
The flaw represents a high-severity threat, earning a CVSS score of 7.2, and affects the 16-bit and 32-bit implementations of the instruction across multiple product lines.
The vulnerability stems from improper handling of insufficient entropy in AMD CPUs. The RDSEED instruction can return zero values while incorrectly signaling success with a carry flag (CF=1), misleading software into believing it received valid random data.
This misclassification of failure as success creates a dangerous scenario where applications relying on the instruction may consume insufficiently random values, potentially compromising cryptographic operations and system security.
Understanding the Technical Impact
The technical implications are particularly concerning for security-critical applications.
When RDSEED incorrectly signals successful completion while returning predictable values, cryptographic keys and security tokens generated using this instruction become vulnerable to prediction attacks.
A local attacker with sufficient privileges could potentially influence the values returned by RDSEED, further degrading randomness quality and potentially breaking the integrity of security mechanisms that depend on true randomness.
Notably, the vulnerability affects only the 16-bit and 32-bit forms of RDSEED.
The 64-bit variant remains unaffected, providing a potential temporary workaround for some applications. AMD plans to release microcode patches to remediate this issue across affected processors.
Immediate Workarounds Available
Until microcode patches become available, AMD recommends three immediate mitigation strategies.
Organizations can switch to the 64-bit form of RDSEED to avoid the vulnerable implementations.
Alternatively, administrators can mask the RDSEED capability from software discovery using the clearcpuid=rdseed boot parameter or QEMU command-line options.
A third option involves treating RDSEED returns of zero as failures and retrying the instruction until valid random values appear.
AMD plans to distribute fixes through Original Equipment Manufacturers by targeted release dates.
AMD EPYC 9005 Series processors are scheduled to receive microcode updates in late October 2025, with AGESA mitigations following by November 14, 2025.
Consumer-facing products, including Ryzen 9000 Series Desktop, Ryzen 9000HX, and Ryzen AI processors, have mitigation releases targeted for late November 2025.
The vulnerability initially surfaced on the Linux kernel mailing list before formal AMD notification, highlighting the importance of coordinated vulnerability disclosure in the security community.
Organizations running AMD Zen 5-based systems should prioritize applying available patches and implementing recommended workarounds to maintain cryptographic integrity and system security.
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