CVE-2026-16158 @fastify/reply-from vulnerable to cross-upstream request routing via URL cache key collision
An attacker can cause cross-upstream data access and modification due to URL cache key collisions in the Fastify reply-from plugin.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-16158?
CVE-2026-16158 is a high-severity vulnerability in @fastify/reply-from, published on 18 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-441
Which versions are affected by CVE-2026-16158?
It affects 1 product.
Products include Fastify Fastify\/Reply-From.
How do I fix CVE-2026-16158?
No fix has been published for CVE-2026-16158 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-16158 being exploited?
There is no known exploitation of CVE-2026-16158 in the wild and no public exploit code.
Sources
Also known as GHSA-v574-6498-x57v.