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Fencer Intel
high 8.8

CVE-2021-33621 json

HTTP response splitting in CGI

published 3y ago modified 2mo ago also BIT-ruby-2021-33621 , BIT-ruby-min-2021-33621 , EUVD-2022-7435 , GHSA-vc47-6rqg-c7f5 , JLSEC-2026-1286

cvss
8.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.5%
EPSS 2.5% chance of exploitation in 30 days, percentile 84%
public exploits
0
none known

Summary

The cgi gem before 0.1.0.2, 0.2.x before 0.2.2, and 0.3.x before 0.3.5 for Ruby allows HTTP response splitting. This is relevant to applications that use untrusted user input either to generate an HTTP response or to create a CGI::Cookie object.

Patch / fix

  • rubygems cgi 0.1.0.2, 0.2.2, 0.3.5
  • bitnami ruby 2.7.7, 3.0.5, 3.1.3
  • bitnami ruby-min 2.7.7, 3.0.5, 3.1.3
  • ruby-lang cgi 0.1.0.2, 0.2.2, 0.3.5
  • ruby-lang ruby 2.7.7, 3.0.5, 3.1.3
  • ruby3.1 Debian 12 3.1.2-4

debian advisories DEBIAN-CVE-2021-33621

  • ruby2.5 Ubuntu 18.04 LTS 2.5.1-1ubuntu1.13
  • ruby2.7 Ubuntu 20.04 LTS 2.7.0-5ubuntu1.8
  • ruby3.0 Ubuntu 22.04 LTS 3.0.2-7ubuntu2.3
  • ruby2.3 Ubuntu Pro 16.04 LTS 2.3.1-2~ubuntu16.04.16+esm4

ubuntu advisories UBUNTU-CVE-2021-33621

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • ruby RHEL 9 3.1.4-143.module+el9.3.0+21558+96b51efd
  • rubygems RHEL 9 3.3.26-143.module+el9.3.0+21558+96b51efd
  • ruby-libs RHEL 9 3.1.4-143.module+el9.3.0+21558+96b51efd
  • rubygem-pg RHEL 9 1.3.5-1.module+el9.1.0+15737+76195479
  • rubygem-irb RHEL 9 1.4.1-143.module+el9.3.0+21558+96b51efd
  • rubygem-rbs RHEL 9 2.7.0-143.module+el9.3.0+21558+96b51efd
  • rubygem-rss RHEL 9 0.2.9-143.module+el9.3.0+21558+96b51efd
  • rubygem-json RHEL 9 2.6.1-143.module+el9.3.0+21558+96b51efd

red hat advisories RHSA-2024:1576RHSA-2024:1431RHSA-2023:7025RHSA-2024:3838RHSA-2024:3500RHSA-2024:4542

  • ruby2.5 SLES for SAP 15 SP3, SLES for SAP 15 SP2, SLES for SAP 15 SP1 +14 more 2.5.9-150000.4.29.1

suse advisories SUSE-SU-2023:4176-1

  • ruby3.1 openSUSE Tumbleweed 3.1.3-1.1

opensuse advisories openSUSE-SU-2024:12539-1

  • ruby AlmaLinux 9 3.0.7-162.el9_4
  • rubygems AlmaLinux 9 3.2.33-162.el9_4
  • ruby-libs AlmaLinux 9 3.0.7-162.el9_4
  • rubygem-irb AlmaLinux 9 1.3.5-162.el9_4
  • rubygem-rbs AlmaLinux 9 1.4.0-162.el9_4
  • rubygem-rss AlmaLinux 9 0.2.9-162.el9_4
  • rubygem-json AlmaLinux 9 2.5.1-162.el9_4
  • rubygem-rake AlmaLinux 9 13.0.3-162.el9_4

almalinux advisories ALSA-2024:3838ALSA-2024:3500ALSA-2024:1576ALSA-2024:1431ALSA-2023:7025ALSA-2023:3821

  • ruby Rocky Linux 8 2.5.9-111.module+el8.9.0+1536+5f79634e
  • rubygem-pg Rocky Linux 8 1.0.0-3.module+el8.9.0+1536+5f79634e
  • rubygem-abrt Rocky Linux 8 0.3.0-4.module+el8.9.0+1536+5f79634e
  • rubygem-abrt Rocky Linux 8 0.3.0-4.module+el8.5.0+738+032c9c02
  • rubygem-bson Rocky Linux 8 4.3.0-2.module+el8.9.0+1536+5f79634e
  • rubygem-mongo Rocky Linux 8 2.5.1-2.module+el8.9.0+1536+5f79634e
  • rubygem-mysql2 Rocky Linux 8 0.4.10-4.module+el8.9.0+1536+5f79634e
  • rubygem-bundler Rocky Linux 8 1.16.1-4.module+el8.9.0+1536+5f79634e

rocky linux advisories RLSA-2023:7025RLSA-2024:1576RLSA-2024:1431RLSA-2023:3821

  • ruby Alpine 3.14 2.7.7-r0
  • ruby Alpine 3.15 3.0.5-r0
  • ruby Alpine 3.24, Alpine 3.23, Alpine 3.22 +6 more 3.1.3-r0

alpine advisories ALPINE-CVE-2021-33621

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2021-33621 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

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-2021-33621 updated cvss 8.8

ruby/cgi-gem: HTTP response splitting in CGI

  • Red Hat Enterprise Linux 6 ruby, ruby-ri, ruby-irb, ruby-libs, ruby-rdoc, ruby-tcltk Red Hat Enterprise Linux 7 ruby, ruby-irb, rubygems, ruby-libs, ruby-tcltk, rubygem-json, +6 more
    affected: no fix planned “Out of support scope”
  • Red Hat Software Collections rh-ruby30-ruby, rh-ruby30-rubygems, rh-ruby30-ruby-libs, rh-ruby30-rubygem-irb, rh-ruby30-rubygem-rbs, rh-ruby30-rubygem-rss, +12 more
    affected: no fix planned “Will not fix”
  • Red Hat CodeReady Linux Builder EUS (v.9.2) ruby-doc 3.0.4-161.el9_2.1
    fixed: vendor fix RHSA-2024:4542
  • Red Hat Enterprise Linux AppStream (v. 8) ruby 2.5.9-111.module+el8.9.0+19193+435404ae, ruby 2.7.8-139.module+el8.8.0+18745+f1bef313, ruby 3.1.4-142.module+el8.9.0+21471+7d1e4a35, ruby 3.0.7-143.module+el8.10.0+21858+d19f3934, rubygem-pg 1.2.3-1.module+el8.3.0+7192+4e3a532a, ruby-irb 2.5.9-111.module+el8.9.0+19193+435404ae, +85 more
    fixed: vendor fix RHSA-2024:3500
  • Red Hat Enterprise Linux AppStream (v. 9) ruby 3.0.7-162.el9_4, ruby-libs 3.0.7-162.el9_4, rubygems 3.2.33-162.el9_4, rubygem-irb 1.3.5-162.el9_4, rubygem-rbs 1.4.0-162.el9_4, rubygem-rss 0.2.9-162.el9_4, +35 more
    fixed: vendor fix RHSA-2024:1576
  • Red Hat Enterprise Linux AppStream EUS (v.9.2) ruby 3.0.4-161.el9_2.1, ruby-libs 3.0.4-161.el9_2.1, rubygems 3.2.33-161.el9_2.1, rubygem-irb 1.3.5-161.el9_2.1, rubygem-rbs 1.4.0-161.el9_2.1, rubygem-rss 0.2.9-161.el9_2.1, +13 more
    fixed: vendor fix RHSA-2024:4542
  • Red Hat Enterprise Linux CRB (v. 9) ruby-doc 3.0.7-162.el9_4
    fixed: vendor fix RHSA-2024:3838
  • Red Hat Software Collections for RHEL Workstation(v. 7) rh-ruby27-ruby 2.7.8-132.el7, rh-ruby27-rubygems 3.1.6-132.el7, rh-ruby27-ruby-libs 2.7.8-132.el7, rh-ruby27-rubygem-irb 1.2.6-132.el7, rh-ruby27-rubygem-json 2.3.0-132.el7, rh-ruby27-rubygem-psych 3.1.0-132.el7, +13 more Red Hat Software Collections for RHEL(v. 7) rh-ruby27-ruby 2.7.8-132.el7, rh-ruby27-rubygems 3.1.6-132.el7, rh-ruby27-ruby-libs 2.7.8-132.el7, rh-ruby27-rubygem-irb 1.2.6-132.el7, rh-ruby27-rubygem-json 2.3.0-132.el7, rh-ruby27-rubygem-psych 3.1.0-132.el7, +13 more
    fixed: vendor fix RHSA-2023:3291

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

2.45% chance of exploitation in the next 30 days, higher than 84% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • ruby-lang.org https://www.ruby-lang.org/en/news/2022/11/22/http-response-splitting-in-cgi-cve-2021-33621/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
GitHub 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
OSV 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
rubygems cgi
>=0.3.0, <0.3.5
>=0.2.0, <0.2.2
<0.1.0.2
0.3.5
0.2.2
0.1.0.2
bitnami ruby
>=2.7.0, <2.7.7
>=3.0.0, <3.0.5
>=3.1.0, <3.1.3
2.7.7
3.0.5
3.1.3
bitnami ruby-min
>=2.7.0, <2.7.7
>=3.0.0, <3.0.5
>=3.1.0, <3.1.3
2.7.7
3.0.5
3.1.3
julia ruby_jll
all versions
 no fix listed

Classification

Weakness
  • CWE-436 Interpretation Conflict
  • CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component

References

Sources

Fencer Intel 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.