How severe is CVE-2021-21322?

CVE-2021-21322 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-2021-21322 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-21322?

CVE-2021-21322 affects Fastify-http-proxy Project Fastify-http-proxy. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-21322?

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-2021-21322 published?

CVE-2021-21322 was published on 2021-03-02 and last updated on 2026-06-17.

CVE-2021-21322

CVE-2021-21322 is a critical-severity vulnerability in Fastify-http-proxy Project 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)
CVSS v2: 7.5
EPSS exploit prediction: 2% (74th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Fastify-http-proxy Project Fastify-http-proxy
Published: 2021-03-02
Last modified: 2026-06-17

Description

fastify-http-proxy is an npm package which is a fastify plugin for proxying your http requests to another server, with hooks. By crafting a specific URL, it is possible to escape the prefix of the proxied backend service. If the base url of the proxied server is `/pub/`, a user expect that accessing `/priv` on the target service would not be possible. In affected versions, it is possible. This is fixed in version 4.3.1.

Frequently asked questions

What is CVE-2021-21322?: fastify-http-proxy is an npm package which is a fastify plugin for proxying your http requests to another server, with hooks. By crafting a specific URL, it is possible to escape the prefix of the proxied backend service. If the base url of the proxied server is `/pub/`, a user expect that accessing `/priv` on the target service would not be possible. In affected versions, it is possible. This is fixed in version 4.3.1.
How severe is CVE-2021-21322?: CVE-2021-21322 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-2021-21322 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21322?: CVE-2021-21322 affects Fastify-http-proxy Project Fastify-http-proxy. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-21322?: 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-2021-21322 published?: CVE-2021-21322 was published on 2021-03-02 and last updated on 2026-06-17.

References

Affected products (1)

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

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