Server-side rendering is the process of turning input data into a displayable form on the server before it reaches the browser. In practice, this can mean generating a preview, diff, report, notebook view, or email template from content supplied by a user or another system.
In cyber security, it matters because rendering is not just presentation: it is a parsing and transformation step that sits inside the trust boundary. If attackers can feed malformed files or crafted text into a renderer, they may trigger injection flaws, template misuse, or memory corruption in native libraries used during conversion. Defenders reduce risk by treating rendered content as untrusted input, restricting privileges, patching dependencies, validating formats, sandboxing complex parsers, and separating display logic from sensitive services.