Unintended Proxy or Intermediary ('Confused Deputy') Affecting @fastify/reply-from package, versions >=8.3.1 <12.6.4
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JS-FASTIFYREPLYFROM-18016324
- published19 Jul 2026
- disclosed18 Jul 2026
- creditHamdaanAliQuatil
Introduced: 18 Jul 2026
NewCVE-2026-16158 (opens in a new tab)How to fix?
Upgrade @fastify/reply-from to version 12.6.4 or higher.
Overview
@fastify/reply-from is a forward your HTTP request to another server, for fastify
Affected versions of this package are vulnerable to Unintended Proxy or Intermediary ('Confused Deputy') in the getUpstream function. An attacker can gain unauthorized access to or modify data across different upstreams by exploiting a URL cache key collision, which occurs when different destination and source path pairs generate the same cache key due to the lack of a delimiter. This allows cached URLs for one upstream to be reused for requests intended for another upstream.
Workaround
This vulnerability can be mitigated by passing disableCache: true when registering the plugin.