CVE-2015-2666

What it actually does

The vulnerability is a stack-based buffer overflow in the get_matching_model_microcode function that processes microcode headers from the initrd, enabling local privilege escalation when an attacker has root write access to construct a malicious header.

Why it matters to the business

Attackers with existing local root access can achieve full system compromise on unpatched legacy Linux systems, risking data theft or persistent control; the issue is over a decade old with low exploitability so impact is largely limited to outdated environments that have not been upgraded.

How an attack unfolds

An attacker first obtains root privileges, then plants a crafted microcode header inside the initrd image; on subsequent boot the kernel's early microcode loader triggers the overflow during header parsing and executes attacker-controlled code with kernel privileges.

How to fix it

Upgrade the Linux kernel to version 4.0 or later on all affected distributions; rebuild and reinstall the initrd after the update.

How to confirm the fix worked

Confirm the running kernel version is 4.0 or newer, then verify that microcode loading completes without crashes when a malformed header is present in the initrd.

Typical attack path

1. Obtain local root access on the target host
2. Write a malicious microcode header into the initrd
3. Trigger kernel boot or microcode reload to reach the vulnerable function
4. Execute arbitrary code via the resulting stack overflow

How to detect it

Review boot logs for microcode-related crashes or unexpected privilege changes, and inspect initrd contents on any remaining unpatched systems for signs of unauthorized modification.

What your security team should do

• Immediately upgrade all systems still running kernels older than 4.0
• Audit and restrict root-level write access to initrd images
• Remove or isolate any remaining legacy systems that cannot be patched