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CVE Record

CVE-2021-4235: Denial of service in gopkg.in/yaml.v2

Due to unbounded alias chasing, a maliciously crafted YAML file can cause the system to consume significant system resources. If parsing user input, this may be used as a denial of service vector.

MediumCVSS 5.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This flaw can let a malicious YAML file make software using go-yaml consume excessive resources and become unavailable. The business impact is service disruption, not data theft or code execution, based on the supplied sources.

Executive priority

Treat as a moderate availability risk. Prioritize externally reachable or automation-critical systems that parse untrusted YAML, especially CI, import, configuration, or document-processing workflows.

Technical view

CVE-2021-4235 is a denial-of-service issue in go-yaml/yaml.v2 caused by unbounded alias chasing while parsing YAML. The CVSS 3.1 score is 5.5, with high availability impact and no stated confidentiality or integrity impact.

Likely exposure

Exposure is most likely where Go applications parse YAML from users, uploads, repositories, configuration pipelines, or other untrusted sources. Internal-only tooling may still be affected if it processes attacker-controlled files.

Exploitation context

The bundle does not show CISA KEV listing or cited active exploitation. Exploitation requires a crafted YAML document being parsed by an affected component; the provided CVSS vector indicates local attack vector and required user interaction.

Researcher notes

The source evidence supports denial of service through alias handling, with no sourced claim of code execution or active exploitation. Version and remediation details should be confirmed from GO-2021-0061 and upstream go-yaml guidance before closure.

Mitigation direction

  • Inventory Go projects using go-yaml/yaml.v2 or gopkg.in/yaml.v2.
  • Check Go vulnerability database and vendor guidance for fixed versions.
  • Update affected dependencies according to vendor guidance.
  • Avoid parsing untrusted YAML where possible.
  • Apply input size and resource limits around YAML processing.

Validation and detection

  • Search dependency manifests for go-yaml/yaml and gopkg.in/yaml.v2.
  • Confirm resolved versions against GO-2021-0061 vendor guidance.
  • Identify code paths parsing YAML from user-controlled sources.
  • Review service monitoring for YAML parsing resource spikes.
  • Confirm DoS controls exist for upload or config ingestion paths.
Prepared
Confidence
medium
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

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CVE-2021-4235 mapping review

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

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.5 (3.1)
Known Exploited
No
Published

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

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
5Source 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
5.5CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H1.83.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

5.5Medium
CVSS 3.1 vector shape for CVE-2021-4235Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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
gopkg.in/yaml.v2gopkg.in/yaml.v2gopkg.in/yaml.v2, 0unaffected
github.com/go-yaml/yamlgithub.com/go-yaml/yamlgithub.com/go-yaml/yamlaffected
Weakness

CWE details

No CWE listed

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