LiveActive security incident?Get immediate response
CVE Record

CVE-2021-33621: 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 splitt...

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.

UnknownCVSS not scoredNot KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-33621 is an HTTP response splitting flaw in Ruby's cgi gem. Business risk is mainly for Ruby applications that place untrusted input into HTTP responses or CGI::Cookie objects. Successful abuse could let an attacker influence response headers, but impact depends heavily on application behavior.

Executive priority

Prioritize normal vulnerability remediation for Ruby internet-facing services and packaged appliances that include Ruby. Escalate only if code review finds untrusted input reaching affected response or cookie generation paths.

Technical view

The affected cgi gem versions are before 0.1.0.2, 0.2.x before 0.2.2, and 0.3.x before 0.3.5. The flaw is relevant where untrusted user input is used to generate HTTP responses or create CGI::Cookie objects. The bundle provides no CVSS, CWE, or exploitability metric.

Likely exposure

Exposure is likely limited to Ruby applications or packaged Ruby runtimes using vulnerable cgi gem versions with reachable untrusted input in response or cookie generation paths.

Exploitation context

The source bundle does not show CISA KEV listing or cited evidence of active exploitation. Treat this as a patching and code-audit issue, not a confirmed exploited-in-the-wild emergency.

Researcher notes

The public record identifies affected version ranges and the vulnerable usage pattern, but lacks CVSS, CWE, and exploitation evidence. Validation should focus on dependency versioning plus whether attacker-controlled input reaches cgi response or cookie construction.

Mitigation direction

  • Upgrade cgi to 0.1.0.2, 0.2.2, 0.3.5, or later as applicable.
  • Apply Ruby package updates from your operating system vendor.
  • Audit code using CGI::Cookie with user-controlled values.
  • Avoid placing raw untrusted input into response header or cookie construction paths.
  • Check Ruby and distribution advisories for environment-specific guidance.

Validation and detection

  • Inventory Ruby applications and dependency locks for cgi gem versions.
  • Check OS package versions where Ruby is supplied by Fedora, Debian, Gentoo, or vendors.
  • Review request handlers that construct responses or CGI::Cookie objects.
  • Confirm patched versions are deployed in production and build images.
  • Record no active exploitation claim unless new authoritative evidence appears.
Prepared
Confidence
high
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2021-33621 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
9Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.