How severe is CVE-2026-16117?

CVE-2026-16117 has a CVSS 3.x base score of 10.0, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-16117 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (19th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-16117?

CVE-2026-16117 affects Fastify Fastify/http-proxy. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-16117?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2026-16117 published?

CVE-2026-16117 was published on 2026-07-18 and last updated on 2026-07-28.

CVE-2026-16117

CVE-2026-16117 is a critical-severity vulnerability in Fastify Fastify/http-proxy with a CVSS 3.x base score of 10.0. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Critical (CVSS 3.x base score 10.0)
EPSS exploit prediction: 0% (19th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Fastify Fastify/http-proxy
Published: 2026-07-18
Last modified: 2026-07-28

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.

Frequently asked questions

What is CVE-2026-16117?: 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.
How severe is CVE-2026-16117?: CVE-2026-16117 has a CVSS 3.x base score of 10.0, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-16117 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (19th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-16117?: CVE-2026-16117 affects Fastify Fastify/http-proxy. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-16117?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2026-16117 published?: CVE-2026-16117 was published on 2026-07-18 and last updated on 2026-07-28.

References

Affected products (1)

cpe:2.3:a:fastify:fastify\/http-proxy:*:*:*:*:*:node.js:*:*

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