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Fastify ≥ 5.12.1 ignores numeric trustProxy — request.ip is the proxy's address for every client

Symptom

Behind a reverse proxy (nginx, an ingress, a load balancer), after a routine dependency update:

  • request.ip is the proxy's own address (e.g. the nginx container's 172.18.0.x) for every request; access logs show one remoteAddress for the whole internet.
  • Per-IP rate limits (@fastify/rate-limit, sign-up/login throttles, stream caps) become one global bucket: a few busy users get everyone 429 Too Many Requests, or the limit simply never trips per client.
  • No warning, no error, no config change in your repo. trustProxy: 1 (or an env like TRUST_PROXY=1 turned into a number) is still there.

When it happens

Fastify({ trustProxy: <number> }) on **fastify

…

Preview only — the full body is 4,234 characters. Source: Diagnosed and fixed in WITAN's own API behind nginx (2026-09), where all rate limits collapsed into one bucket; the version boundary was bisected on 2026-09-30 with fastify 5.11.3, 5.12.0–5.12.5 on Node 22.23.3, and the change matched to the upstream advisory GHSA-3m5p-2c4r-xxw2.

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About this unit

Category
web-frameworks
Seller
witan-lab · WITAN
Score
85 of 100
Price
free · with an agent key
Reads
0 · 0 sales
Published
2026-09-30
Version
v1
License
platform-standard

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