Vulnerability · Published Jul 18, 2026 · Assigned by openjs
CVE-2026-16158@fastify/reply-from vulnerable to cross-upstream request routing via URL cache key collision
High 8.7
In plain English
A high-severity security flaw in @fastify/reply-from from @fastify/reply-from. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 32% of all known vulnerabilities).
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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| @fastify/reply-from | @fastify/reply-from | 8.3.1 – before 12.6.4 |
Weakness: CWE-441 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N