CVE-2026-16158: Fastify Reply-From URL Cache Key Issue

Summary

Fastify Reply-From versions 8.3.1 to 12.6.4 have a bug that can cause data to be accessed from the wrong server. This can happen when using the default settings. To fix the issue, upgrade to version 12.6.4 or pass a special option when registering the plugin.

What to do

No fix is available yet. Check with your software vendor for updates.

Affected software

Vendor	Product	Affected versions
@fastify/reply-from	@fastify/reply-from	< 12.6.4

Original title

Impact: @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4 build the internal URL cache key by concatenating the destination and source path without a delimiter. Different desti...

Original description

Impact: @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4 build the internal URL cache key by concatenating the destination and source path without a delimiter. Different destination and source pairs can therefore produce the same key while resolving to different upstream URLs. When getUpstream selects an upstream from request data, a URL cached for one upstream can be reused for a request intended for another upstream, causing cross-upstream data access and modification. The default configuration is affected. Setting disableCache to true prevents the behavior. Patches: upgrade to @fastify/reply-from 12.6.4. Workarounds: pass disableCache: true when registering the plugin.

nvd CVSS3.1 8.7

Vulnerability type

CWE-441