What is CVE-2026-16158?

CVE-2026-16158 is a high-severity vulnerability in Fastify Fastify\/reply-From, classified under Unintended Proxy or Intermediary (Confused Deputy). CVSS score: 8.7/10. Published 2026-07-18.

How severe is CVE-2026-16158?

High severity. CVSS v3 base score is 8.7 out of 10.

Vulnerability in Fastify Fastify\/reply-From

CVE-2026-16158

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.

EPSS: 0.002 (13.8th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 8.7 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N.

Affected products

Fastify Fastify\/reply-from
@Fastify/reply-from — versions 8.3.1, 12.6.4

Weakness classification (CWE)

CWE-441 — Unintended Proxy or Intermediary (Confused Deputy)

References

ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)
ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)

Frequently asked questions

What is CVE-2026-16158?: CVE-2026-16158 is a high-severity vulnerability in Fastify Fastify\/reply-From, classified under Unintended Proxy or Intermediary (Confused Deputy). CVSS score: 8.7/10. Published 2026-07-18.
How severe is CVE-2026-16158?: High severity. CVSS v3 base score is 8.7 out of 10.