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CVE-2021-41819: CGI::Cookie.parse in Ruby through 2.6.8 mishandles security prefixes in cookie names.

CGI::Cookie.parse in Ruby through 2.6.8 mishandles security prefixes in cookie names. This also affects the CGI gem through 0.3.0 for Ruby.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This Ruby CGI cookie parsing flaw can let cookie names that appear protected by browser security prefixes be mishandled. Applications that trust those parsed cookies for security decisions could face integrity risk, such as accepting attacker-controlled cookie values as more trusted than intended.

Executive priority

Treat as a high-priority dependency and platform patching item for Ruby web applications. Urgency rises when cookies drive authentication, authorization, session selection, or other integrity-sensitive decisions.

Technical view

CVE-2021-41819 affects CGI::Cookie.parse in Ruby through 2.6.8 and the CGI gem through 0.3.0. The issue is cookie prefix spoofing involving security-prefixed cookie names. CVSS 3.1 is 7.5, network exploitable, no privileges or user interaction, with high integrity impact.

Likely exposure

Exposure is most likely in Ruby applications or bundled products using CGI::Cookie.parse or the affected CGI gem to parse HTTP Cookie headers, especially where parsed cookies influence authentication, session, tenant, or trust decisions.

Exploitation context

The bundle does not show CISA KEV listing or confirmed active exploitation. The risk is practical where an attacker can send HTTP requests with crafted Cookie headers and the application trusts the parser’s output for security-sensitive logic.

Researcher notes

The affected range is clear from the bundle, but product-level exposure is not. Focus validation on reachable HTTP cookie parsing paths and downstream trust decisions. Do not assume exploit activity without KEV or advisory evidence.

Mitigation direction

  • Identify Ruby runtimes through 2.6.8 and CGI gem versions through 0.3.0.
  • Apply Ruby, CGI gem, or operating-system vendor updates from official advisories.
  • Review security-sensitive code that consumes CGI::Cookie.parse output.
  • Avoid relying on parsed cookie names alone for authorization or session trust.
  • Check vendor guidance for bundled products, including NetApp advisories if relevant.

Validation and detection

  • Inventory Ruby versions and CGI gem versions in production and build images.
  • Search application code for CGI::Cookie.parse usage.
  • Confirm patched packages from Ruby, Fedora, Gentoo, or applicable vendor channels.
  • Review tests covering duplicate or security-prefixed cookie parsing behavior.
  • Validate session and authorization logic does not trust spoofable cookie input.
Prepared
Confidence
medium
Sources
8

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

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cwe · low confidence lookup

CWE-565: Exact CWE lookup

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cve · low confidence lookup

CVE-2021-41819 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

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

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.

1CVSS vectors
0Timeline events
0ADP providers
7Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N3.93.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2021-41819Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

CWE-565

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

CWE-565 · source CWE mapping

Reliance on Cookies without Validation and Integrity Checking

Reliance on Cookies without Validation and Integrity Checking represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs