CVE-2026-16117: Fastify Fastify/http-proxy vulnerability (CVSS 10.0)

Description

Impact: @fastify/http-proxy versions up to and including 11.5.0 fail to rewrite the request prefix when the prefix segment is URL-encoded. Fastify's router URL-decodes paths for route matching, but request.url retains the original encoded form, and the prefix-rewrite step uses a literal string replace against the decoded prefix. A request that encodes one or more characters of the configured prefix therefore matches the route but skips the rewrite, so the raw encoded path is forwarded to the upstream unchanged. The upstream then decodes the path and serves it, letting an attacker reach upstream paths that the proxy was configured to hide via rewritePrefix, including internal or administrative endpoints. Patches: upgrade to @fastify/http-proxy 11.6.0. Workarounds: none.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeChanged

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

Affected products

Fastify Fastify/http-proxy< 11.6.0

Remediation

Fixed in

Fastify Fastify/http-proxy≥ 11.6.0

Patch & vendor advisories

References

https://cna.openjsf.org/security-advisories.htmlVendor Advisory
https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-mx7v-qhg9-2mvvVendor Advisory

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-16117 being actively exploited?

CVE-2026-16117 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.44%.

How severe is CVE-2026-16117?

CVE-2026-16117 has a CVSS 3.1 base score of 10.0, rated critical. EPSS estimates a 0.44% probability of exploitation.

Which products are affected by CVE-2026-16117?

Affected products include Fastify Fastify/http-proxy.

How do I fix CVE-2026-16117?

Upgrade affected software to a fixed version, for example Fastify Fastify/http-proxy 11.6.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-16117 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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