API10:2023 — Unsafe Consumption of APIs

Slide 8 · Context

API10 closes the loop: APIs aren’t just servers. They’re also clients — and clients can be exploited too.

Why this risk is at the end of the list — and why that doesn’t mean it’s rare or minor.

Why it’s #10

API10 requires a multi-step attack: compromise or impersonate a third-party, then leverage the consuming API’s trust to deliver a payload. This is more complex than directly exploiting the target API — hence its position at #10 in exploitability. But its impact is severe: the Magecart supply chain campaign compromised over 100 organizations between 2015 and 2020. The attack surface is also growing as APIs integrate more third-party services.

Direct API attack (API1–API9)

Attacker sends malicious input to the target API

Target API has input validation at its boundary

Attack must bypass the API’s own defenses

One target, one attack surface

Supply chain attack (API10)

Attacker compromises a third-party the target trusts

Malicious data enters through a trusted channel

Bypasses input validation (applied to user input, not third-party input)

One compromise, many downstream targets

Scale advantage for attackers

Supply chain attacks scale in a way direct attacks don’t. Compromising Inbenta’s CDN reached all of Inbenta’s clients simultaneously. Compromising a widely-used npm package, a popular analytics script, or a shared API gateway can deliver a malicious payload to hundreds or thousands of consuming APIs with a single compromise. This is why API10 is serious despite its lower exploitability score.

← Back How do attacks work? →