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CVE-2021-21322

30
FAUCET Score

CVE-2021-21322 is a critical vulnerability affecting the fastify-http-proxy npm package, a Fastify plugin for HTTP request proxying. This flaw allows an attacker to bypass intended URL prefix restrictions, enabling access to unauthorized backend services by crafting a specific URL. With a CVSS score of 9.8 (CRITICAL), it presents a severe risk due to its network-based attack vector, low complexity, and potential for complete compromise of confidentiality, integrity, and availability. While no active exploitation, public exploit code, or significant community discussion has been observed, the vulnerability is patched in version 4.3.1.

Impacted Technologies

VendorProductVersion(s)CPE
< 4.3.1CPE matchmatch criteria
cpe:2.3:a:fastify-http-proxy_project:fastify-http-proxy:*:*:*:*:*:node.js:*:*

CVSS Data

CVSS version used by this source: 3.1

10.0CRITICAL

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
5.8
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.61%
Probability of exploitation in next 30 days
EPSS Percentile
73.5%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0161 is in the 61st percentile among its peer group of 36,862 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (3)

github_advisorypatch availablevia nvd_reference
View patch
npmpatch availablevia ghsa
Product: fastify-http-proxyFixed in: 4.3.1
redhatno patchvia redhat_api
Product: Red Hat Advanced Cluster Management for Kubernetes 2Fixed in: rhacm2/search-ui-rhel8

Vendor Advisories (2)

npmGHSA-c4qr-gmr9-v23wlow

Prefix escape

Mar 3, 2021
redhatCVE-2021-21322Critical

fastify-http-proxy: crafted URL allows prefix scape of the proxied backend service

Feb 23, 2021

References

github.com / fastify/fastify-http-proxy/commit/02d9b43c770aa16bc44470edecfaeb7c17985016
PatchThird Party Advisory
github.com / fastify/fastify-http-proxy/security/advisories/GHSA-c4qr-gmr9-v23w
Third Party Advisory
npmjs.com / package/fastify-http-proxy
ProductThird Party Advisory