CVE-2021-21322

Name: CVE-2021-21322
Creator: NVD / NIST
Published: 2021-03-02T04:15:12.597+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 1.92%

Last modified Jun 17, 2026

CVE-2021-21322 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. 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. EPSS estimates a 1.92% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

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

EPSS Probability

1.92%

77.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-20

Affected Software

Vendor	Product	Versions
Fastify-Http-Proxy Project	Fastify-Http-Proxy	< 4.3.1

References

https://github.com/fastify/fastify-http-proxy/commit/02d9b43c770aa16bc44470edecfaeb7c17985016Patch, Third Party Advisory
https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-c4qr-gmr9-v23wThird Party Advisory
https://www.npmjs.com/package/fastify-http-proxyProduct, Third Party Advisory
https://github.com/fastify/fastify-http-proxy/commit/02d9b43c770aa16bc44470edecfaeb7c17985016Patch, Third Party Advisory
https://github.com/fastify/fastify-http-proxy/security/advisories/GHSA-c4qr-gmr9-v23wThird Party Advisory
https://www.npmjs.com/package/fastify-http-proxyProduct, Third Party Advisory

Timeline

Published: Mar 2, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-21322?

How severe is CVE-2021-21322?

CVE-2021-21322 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 1.92% probability of exploitation in the next 30 days.

How do I fix CVE-2021-21322?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-21322?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST