AIKIDO-2026-247087
@fastify/reply-from is vulnerable to Confused Deputy
87
High Risk
This Affects:
@fastify/reply-fromTL;DR
@fastify/reply-from builds its internal URL cache key by concatenating the destination and source path without a delimiter. Because there is no separator, different destination and source pairs can produce the same cache key while resolving to different upstream URLs. When an application uses the getUpstream() option with the default URL cache enabled, a request can be silently forwarded to the wrong upstream, causing unauthorized cross-upstream data access and modification. The fix derives the cache key from a structured value so distinct pairs no longer collide.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and your application uses the getUpstream() option to route between multiple upstreams with the default URL cache enabled.
Background info
@fastify/reply-from is vulnerable to Confused Deputy in versions 8.3.1 - 12.6.3.
How to fix this
Upgrade the @fastify/reply-from library to the patch version.
Links
GitHub Release
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SOC 2Compliant
ISO 27001Compliant