Open Redirect

published 2021-09-12 5 y ago modified 2026-07-08 4 mo ago also GHSA-4hpq-rjcx-7vj9 , EUVD-2021-1974

cvss: 7.6; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.7%; EPSS 0.7% chance of exploitation in 30 days, percentile 53%
public exploits: 0; none known

This affects the package clearance before 2.5.0. The vulnerability can be possible when users are able to set the value of session[:return_to]. If the value used for return_to contains multiple leading slashes (/////example.com) the user ends up being redirected to the external domain that comes after the slashes (http://example.com).

Patch / fix

fixed in 2 links 1

rubygems clearance 2.5.0
n/a clearance 2.5.0

github.com/thoughtbot/clearance#945 pull request

Exploit prediction

0.70% chance of exploitation in the next 30 days, higher than 53% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	7.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H
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	7.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H

Affected packages

ecosystem	package	affected	fixed in
rubygems	clearance	<2.5.0	2.5.0

Affected products

n/a clearance

Classification

Weakness

CWE-601 URL Redirection to Untrusted Site

References

github.com /thoughtbot/clearance/pull/945
web, patch, third-party-advisory
snyk.io /vuln/SNYK-RUBY-CLEARANCE-1577284
web, third-party-advisory
nvd.nist.gov /vuln/detail/CVE-2021-23435
advisory
github.com /advisories/GHSA-4hpq-rjcx-7vj9
advisory
github.com /rubysec/ruby-advisory-db/blob/master/gems/clearance/CVE-2021-23435.yml
web
github.com /thoughtbot/clearance
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