API Security in 2026: 7 Mistakes Backend Engineers Still Make

Hey devs 👋 I run penetration tests on production APIs for a living, and I keep seeing the same seven security mistakes — even from teams that pride themselves on "shifting left." These aren't exotic flaws. They're patterns I find in 8 out of 10 engagements. Here are the seven, in rough order of how often I find them. If your API has even three of these, you've got real exposure. Trusting Client-Side Authorization This is the #1 vulnerability I find. The frontend hides the 'Admin Panel' button i