CVE-2025-68313

Root

Cause

A hardware defect in AMD Zen5 processors causes the RDSEED instruction's 16-bit and 32-bit register output variants to return a random value of zero at a rate inconsistent with randomness. Critically, the processor incorrectly signals success by setting the carry flag (CF=1), misleading software into trusting the returned value. This issue is documented in AMD-SB-7055 [1].

Exploitation

The vulnerability is inherent to the CPU hardware and can be triggered by any software that uses RDSEED to obtain random numbers. No authentication or special privileges are required; any user process executing RDSEED on an affected Zen5 core may receive a zero value while the CPU reports success. The attack surface includes cryptographic applications, secure key generation, and any system relying on hardware random number generation for security.

Impact

An attacker who can observe or influence the output of RDSEED on an affected system may force the use of a known zero value instead of unpredictable randomness. This could weaken cryptographic operations, compromise key material, or undermine security protocols that depend on high-quality entropy. The bug degrades the trustworthiness of the hardware random number generator.

Mitigation

The fix involves a microcode update that adds revision checking to ensure the RDSEED instruction behaves correctly. The patch has been applied to the stable Linux kernel tree [1]. Users should update their systems with the latest microcode and kernel patches to resolve the issue. No workaround is available without a microcode update.