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CVE-2021-33621

29
FAUCET Score

CVE-2021-33621 is an HTTP response splitting vulnerability affecting the CGI gem for Ruby, specifically versions before 0.1.0.2, 0.2.2, and 0.3.5, impacting applications that process untrusted user input. With a CVSS score of 8.8 (HIGH), it allows an attacker to inject malicious content into HTTP responses, potentially leading to data compromise, integrity issues, and denial of service. While no active exploits or public exploit code (Metasploit, Nuclei, ExploitDB) are reported, it has garnered some community discussion and media coverage, indicating awareness within the cybersecurity community.

Impacted Technologies

VendorProductVersion(s)CPE
< 0.1.0.2CPE matchmatch criteria
cpe:2.3:a:ruby-lang:cgi:*:*:*:*:*:ruby:*:*
>= 0.2.0, < 0.2.2CPE matchmatch criteria
cpe:2.3:a:ruby-lang:cgi:*:*:*:*:*:ruby:*:*
>= 0.3.0, < 0.3.5CPE matchmatch criteria
cpe:2.3:a:ruby-lang:cgi:*:*:*:*:*:ruby:*:*
35CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
36CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:36:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

8.8HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
2.8
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
2.29%
Probability of exploitation in next 30 days
EPSS Percentile
81.4%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0229 is in the 80th percentile among its peer group of 17,844 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.3 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (12)

redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 9Fixed in: ruby-0:3.0.7-162.el9_4
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 9.2 Extended Update SupportFixed in: ruby-0:3.0.4-161.el9_2.1
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-ruby27-ruby-0:2.7.8-132.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: ruby:2.7-8080020230427102918.63b34585
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: ruby:2.5-8090020230627084142.b46abd14
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: ruby:3.1-8090020240311122605.a75119d5
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: ruby:3.0-8100020240522072634.489197e6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 9Fixed in: ruby:3.1-9030020240320163942.9
View patch
rubygemspatch availablevia ghsa
Product: cgiFixed in: 0.3.5
rubygemspatch availablevia ghsa
Product: cgiFixed in: 0.2.2
rubygemspatch availablevia ghsa
Product: cgiFixed in: 0.1.0.2
redhatend of lifevia redhat_api
Product: Red Hat Software CollectionsFixed in: rh-ruby30-ruby

Vendor Advisories (2)

rubygemsGHSA-vc47-6rqg-c7f5high

HTTP response splitting in CGI

Nov 19, 2022
redhatCVE-2021-33621Moderate

ruby/cgi-gem: HTTP response splitting in CGI

Nov 18, 2022

References

lists.debian.org / debian-lts-announce/2024/09/msg00000.html
lists.debian.org / debian-lts-announce/2023/06/msg00012.html
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/DQR7LWED6VAPD5ATYOBZIGJQPCUBRJBX
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/THVTYHHEOVLQFCFHWURZYO7PVUPBHRZD
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/YACE6ORF2QBXXBK2V2CM36D7TZMEJVAS
security.gentoo.org / glsa/202401-27
security.netapp.com / advisory/ntap-20221228-0004
Third Party Advisory
ruby-lang.org / en/news/2022/11/22/http-response-splitting-in-cgi-cve-2021-33621
ExploitThird Party Advisory