A build server is the system that coordinates compilation, testing, packaging, and release steps in a software pipeline. It often runs automated jobs, stores build artifacts, and uses credentials to fetch code, sign outputs, or trigger deployments. Because it sits in the middle of the delivery process, it can influence what software is produced and what later systems accept as trusted.
In cyber security, build servers are high-value targets. If an attacker compromises one, they may tamper with source, inject malicious code into artifacts, steal secrets, or alter release workflows. Defenders treat these systems as part of the trust boundary: limit internet exposure, patch quickly, use least privilege, separate secrets from build jobs, and monitor for unusual agent registration, job changes, or unexpected build activity.