Subj : AMD confirms some Zen 5 CPUs have a worrying security flaw that c
To   : All
From : TechnologyDaily
Date : Tue Nov 04 2025 17:15:07

AMD confirms some Zen 5 CPUs have a worrying security flaw that could put 
users at risk

Date:
Tue, 04 Nov 2025 17:03:00 +0000

Description:
AMD finds a vulnerability in the RDSEED hardware-based random number 
generator.

FULL STORY
======================================================================AMD Zen 
5 chips have a flaw in RDSEED which risks cryptographic key integrity Faulty 
RDSEED may return zeroes, enabling attackers to reconstruct private keys and 
break encryption AMD advises fallback to 64-bit RDSEED or software 
alternatives 

Some AMD processors, including those built on the latest Zen 5 architecture, 
carry a critical vulnerability which affects cryptographic operations and 
thus puts the integrity of protected data at serious risk. 

In a security bulletin, AMD detailed a flaw labeled as AMD-SB-7055, 
describing it as a vulnerability in the RDSEED hardware-based random number 
generator. 

On affected chips, the 16-bit and 32-bit forms of the RDSEED instruction may 
return 0 at a rate thats not entirely random while, at the same time, 
labeling the process as a success. In theory, if a company runs a server that 
generates cryptographic keys for encrypting customer data, and the software 
running on that server uses RDSEED instructions to get random numbers 
directly from the chip, the instruction might return all zeroes. Patches and 
mitigations 

Even though it obviously isnt all random, it would still signal that it 
succeeded, raising absolutely no red flags. 

As a result, attackers who obtain one of the public keys can mathematically 
reconstruct or guess the private key, breaking encryption or impersonating 
the company, meaning encrypted customer records, API tokens, or even 
software-update signatures could be forged or decrypted. 

Mitigations and patches are already in the works. By January 2026, depending 
on the CPU, most should have been mitigated. 

Fixes for AMD's consumer-based Zen 5 chips, including the Ryzen 9000 series, 
AI Max 300 series, Threadripper 9000 series, and Ryzen Z2 series, are coming 
out on November 25. 

AMD added it should have the necessary AGESA microcode updates out soon to 
rectify this issue across all Zen 5 CPUs. 

If youre running chips that dont have a working mitigation just yet, AMD 
recommends you switch back to its unaffected 64-bit form of RDSEED, or move 
to a software failback until it is released. 

 Via Tom's Hardware 

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======================================================================
Link to news story:
https://www.techradar.com/pro/security/amd-confirms-some-zen-5-cpus-have-a-wor
rying-security-flaw-that-could-put-users-at-risk


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