CVE-2026-16158: @fastify/reply-from vulnerable to cross-upstream request routing via URL cache key collision
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 Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
@fastify/reply-fromto a version that resolves this vulnerability.Fixed in 12.6.4 - Configuration
When registering the plugin, set disableCache to true to prevent internal URL cache key collision behavior across upstreams.
@fastify/reply-from disableCache = true
Event History
Frequently Asked Questions
What is the severity of CVE-2026-16158?
CVE-2026-16158 has a high severity rating of 8.7.
What impact does CVE-2026-16158 have?
CVE-2026-16158 can lead to cross-upstream request routing due to URL cache key collisions.
How do I fix CVE-2026-16158?
To fix CVE-2026-16158, upgrade @fastify/reply-from to version 12.6.4 or higher.
Which versions are affected by CVE-2026-16158?
CVE-2026-16158 affects @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4.
What is the vulnerability type of CVE-2026-16158?
CVE-2026-16158 is categorized as a cross-request routing vulnerability.