Cyber Resilience

CVE-2021-33621

HighPublic PoC

Published: 18 November 2022

Published
18 November 2022
Modified
04 November 2025
KEV Added
Patch
CVSS Score v3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.0110 78.5th percentile
Risk Priority 18 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2021-33621 is a high-severity Injection (CWE-74) vulnerability in Ruby-Lang Cgi. Its CVSS base score is 8.8 (High).

Operationally, ranked in the top 21.5% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

EU & UK References

Vulnerability details

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.

CWE(s)

Related Threats

No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.

Affected Assets

ruby-lang
cgi
≤ 0.1.0.2 · 0.2.0 — 0.2.2 · 0.3.0 — 0.3.5
fedoraproject
fedora
35, 36, 37
ruby-lang
ruby
2.7.0 — 2.7.7 · 3.0.0 — 3.0.5 · 3.1.0 — 3.1.3

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

addresses: CWE-74

Developer assessments and testing (including injection-focused techniques) identify improper neutralization of special elements, and the verifiable flaw remediation corrects them pre-deployment.

addresses: CWE-74

Identifies indicators of injection attacks (command, SQL, LDAP, etc.) via anomaly and attack monitoring.

References