How severe is CVE-2026-16158?

CVE-2026-16158 has a CVSS 3.x base score of 8.7, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-16158 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-16158?

CVE-2026-16158 affects Fastify Fastify/reply-from. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-16158?

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

When was CVE-2026-16158 published?

CVE-2026-16158 was published on 2026-07-18 and last updated on 2026-08-05.

CVE-2026-16158

CVE-2026-16158 is a high-severity vulnerability in Fastify Fastify/reply-from with a CVSS 3.x base score of 8.7. 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-441.

Key facts

Severity: High (CVSS 3.x base score 8.7)
EPSS exploit prediction: 0% (14th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-441
Affected product: Fastify Fastify/reply-from
Published: 2026-07-18
Last modified: 2026-08-05

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-16158?: CVE-2026-16158 has a CVSS 3.x base score of 8.7, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-16158 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (14th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-16158?: CVE-2026-16158 affects Fastify Fastify/reply-from. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-16158?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2026-16158 published?: CVE-2026-16158 was published on 2026-07-18 and last updated on 2026-08-05.

References

Affected products (1)

cpe:2.3:a:fastify:fastify\/reply-from:*:*:*:*:*:node.js:*:*

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