Security researchers have uncovered a critical vulnerability in AMD Zen CPUs that allows attackers with elevated privileges to load malicious microcode patches, bypassing cryptographic signature checks. Dubbed “EntrySign,” this flaw stems from AMD’s use of the AES-CMAC algorithm as a hash function during microcode validation—a design decision that enables collision attacks and signature forgery. Cyber Security News is a Dedicated News Platform For Cyber News, Cyber Attack News, Hacking News & Vulnerability Analysis. While CMAC provides integrity against passive attackers, it fails catastrophically when adversaries control the AES key—a scenario made feasible through hardware reverse engineering or side-channel attacks. As CPUs increasingly underpin cloud and AI infrastructures, EntrySign highlights the urgent need for agile, updateable cryptographic primitives in silicon, a lesson the industry is now racing to implement. Kaaviya is a Security Editor and fellow reporter with Cyber Security News. EntrySign exposes all Zen 1-4 CPUs to persistent microcode hijacking by attackers with ring-0 access. AMD’s mitigation replaces CMAC with a custom hash and deploys Secure Processor (ASP) checks before x86 cores activate.
This Cyber News was published on cybersecuritynews.com. Publication date: Fri, 07 Mar 2025 08:40:16 +0000