PHP is an open-source programming language and runtime used mainly to execute server-side code for web applications, often generating HTML and interacting with databases, files, sessions, and external services. Its security relevance covers both the PHP runtime and the applications, extensions, and third-party packages that run within it.
PHP releases and bundled or separately installed extensions can contain vulnerabilities, so supported versions and dependencies should be tracked and patched through vulnerability management. More commonly, application flaws arise from unsafe input handling, such as SQL injection, cross-site scripting, file inclusion, or insecure deserialization; these are not automatically prevented by the language. Secure deployments use parameterized database queries, context-appropriate output encoding, strict upload and filesystem controls, protected session and CSRF handling, and least-privilege service accounts. Configuration and dependency changes should be tested, and logs can help identify exploitation of exposed PHP endpoints.