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API10:2023 Unsafe Consumption of APIs

Trusting upstream API responses without validation. The flip-side of SSRF: the server fetches from a third party, then passes the response through to clients (or uses it in security-sensitive logic) without checking the content or origin.

What Vulkro detects​

Vulkro tracks downstream HTTP client responses that flow into the response body or into authorisation logic without schema validation, allowlist, or signature check.

Non-compliant code (examples)​

Express — pass-through of upstream response

app.get('/exchange-rate', async (req, res) => {
  const upstream = await fetch('https://rates.example.com/usd');
  const json = await upstream.json();
  res.json(json);  // no schema check; upstream could inject anything
});

Compliant code (examples)​

Express — schema-validate the upstream payload

const RateSchema = z.object({ usd: z.number(), eur: z.number() });
app.get('/exchange-rate', async (req, res) => {
  const upstream = await fetch('https://rates.example.com/usd');
  const parsed = RateSchema.parse(await upstream.json());  // throws on shape drift
  res.json(parsed);
});

See also​

  • Confidence model - what High, Medium, and Low mean for findings in this category.
  • Safety - what Vulkro does and does not access on your machine.

References​

This page is generated by vulkro rules export <out-dir> from the catalog in src/rule_docs.rs. Edits made by hand are overwritten on the next regeneration.

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