A critical vulnerability has been discovered in several Linux UEFI shims signed with Microsoft’s digital certificate, potentially allowing attackers to bypass Secure Boot and gain unauthorized access to systems. The flaw, which affects 11 outdated shim packages, was found by security researchers at CyberNews.work.
The affected shim packages were created between 2012 and 2017, a time when Linux distributions began adopting UEFI Secure Boot as a security measure to prevent malware from booting alongside the operating system. A shim is essentially a piece of code that sits between the firmware and the operating system, acting as a translator to facilitate communication. By signing shims with their digital certificate, Microsoft trusted these packages, allowing them to run alongside the kernel without being flagged by Secure Boot.
The 11 vulnerable shim packages were signed using a now-expired certificate issued by Microsoft in 2012. This means that attackers can exploit the flaw by creating and signing their own malicious shims with this expired certificate, which would then be accepted as legitimate by systems using these outdated shim packages. In theory, an attacker could use this vulnerability to inject malware into a system during the boot process, potentially leading to compromised data or even takeover of the entire system.
The affected Linux distributions include Ubuntu, Debian, and Fedora, among others. The impact is significant because Secure Boot is intended to prevent malicious code from executing on systems that have implemented it. By bypassing this security feature, attackers could gain a foothold in an otherwise secure system. It’s also worth noting that the vulnerability only affects systems using UEFI firmware with Linux distributions that still rely on these outdated shim packages.
The discovery of this flaw highlights the ongoing importance of maintaining up-to-date software and firmware to ensure system security. Users of affected Linux distributions should immediately check their version numbers for the shim packages and update them as soon as possible to avoid potential exploitation by attackers. Furthermore, system administrators should also review their UEFI firmware settings to ensure that only trusted shims are allowed to run on their systems.
In light of this discovery, it’s clear that maintaining current software and firmware is crucial in preventing such vulnerabilities from being exploited. As AI-powered tools become increasingly prevalent in detecting and mitigating security risks, users would do well to prioritize regular updates and patching to safeguard against emerging threats.
Source: The Hacker News — 2026-07-14