URL Redirection to Untrusted Site ('Open Redirect') in fastify-static

published 2021-10-05 5 y ago modified 2026-06-17 4 mo ago also GHSA-p6vg-p826-qp3v , EUVD-2021-2234

cvss: 6.1; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.2%; EPSS 1.2% chance of exploitation in 30 days, percentile 67%
public exploits: 0; none known

A redirect vulnerability in the fastify-static module version < 4.2.4 allows remote attackers to redirect users to arbitrary websites via a double slash // followed by a domain: http://localhost:3000//google.com/%2e%2e.The issue shows up on all the fastify-static applications that set redirect: true option. By default, it is false.

Patch / fix

fixed in 2

npm fastify-static 4.2.4
fastify fastify-static 4.2.4

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-22963 updated 2026-01-21 cvss 5.3

fastify-static: open redirect via an URL with double slash followed by a domain

Red Hat Advanced Cluster Management for Kubernetes 2 rhacm2/search-ui-rhel8
affected: no fix available

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.17% chance of exploitation in the next 30 days, higher than 67% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

hackerone.com https://hackerone.com/reports/1354255 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
NVD	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD	2.0	5.8	AV:N/AC:M/Au:N/C:P/I:P/A:N
GitHub	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
npm	fastify-static	<4.2.4	4.2.4

Affected products

n/a https://github.com/fastify/fastify-static

Classification

Weakness

CWE-601 URL Redirection to Untrusted Site

References

hackerone.com /reports/1354255
web, exploit, issue-tracking, third-party-advisory
github.com /fastify/fastify-static/security/advisories/GHSA-p6vg-p826-qp3v
web
nvd.nist.gov /vuln/detail/CVE-2021-22963
advisory
github.com /fastify/fastify-static
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary