Microsoft Security Copilot discovered 20 previously unknown zero-day vulnerabilities in the open-source bootloaders GRUB2 and U-Boot — the software that runs before your operating system even loads. HN59 covers that plus CoffeeLoader, a next-generation malware loader evolving from SmokeLoader with evasion tricks researchers had not documented before.
Stories Covered
Microsoft AI Finds 20 Zero-Days in GRUB2, U-Boot, and Bare Box
Microsoft used its AI-powered Security Copilot to discover 20 previously unknown vulnerabilities across GRUB2 (the default Linux bootloader used by Ubuntu and most major distros), U-Boot, and Bare Box (used in embedded and IoT devices). The flaws include integer and buffer overflows in filesystem parsers, command handling issues, and a side channel in cryptographic comparison code.
Why does this matter? If an attacker can compromise the bootloader, they get in before the operating system even initializes — before your antivirus, your EDR, your anything. Bootkit and rootkit infections at this level are essentially unremovable through software alone; the firmware needs to be reflashed. The GRUB2 flaws are especially significant because they could enable bypassing UEFI Secure Boot and installing stealthy bootkits that persist across OS reinstalls. Microsoft notes that AI not only found the flaws but also generated targeted mitigation recommendations — meaningful help for open-source projects run by volunteer contributors with limited patch bandwidth.
CoffeeLoader: Next-Generation Malware Evasion
Since last fall, the well-known SmokeLoader backdoor has been shipping with a new second-stage payload dropper called CoffeeLoader — built specifically to defeat modern endpoint security, digital forensics tools, and behavioral analysis. CoffeeLoader is a loader (software that loads other malware in, like infostealers or RATs) but with evasion techniques researchers documented as genuinely novel. It borrows techniques from multiple existing malware families and combines them in ways that make signature detection and sandbox analysis significantly less effective. This is the kind of tooling that signals a new baseline for what commodity malware can do.
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