CVE-2021-4178

Arbitrary code execution via unsafe YAML deserialization

Published Aug 24, 2022 · Updated Aug 3, 2024

Unsafe YAML deserialization in Fabric8 Kubernetes Client 5.x allows local privileged users to execute arbitrary Java code through malicious YAML. The Serialization.unmarshalYaml method creates SnakeYAML with its default constructor, which accepts attacker-selected Java types while loading input. Exploitation requires a privileged local user to supply a configuration or Kubernetes resource string that an application passes to this parser.

CVSS severity6.7
Medium
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unsafe YAML deserialization in Fabric8 Kubernetes Client 5.x allows local privileged users to execute arbitrary Java code through malicious YAML. The Serialization.unmarshalYaml method creates SnakeYAML with its default constructor, which accepts attacker-selected Java types while loading input. Exploitation requires a privileged local user to supply a configuration or Kubernetes resource string that an application passes to this parser.

The record

CVE
CVE-2021-4178
Published
Aug 24, 2022
Updated
Aug 3, 2024
Vendor
Fabric8
Product
Fabric8 Kubernetes Client
Classifications
CWE-502, CWE-94, T1203
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Aug 24, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Affects 5.x versions, Fixed in kubernetes-client v5.0.3 and above.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

Fabric8 · Fabric8 Kubernetes Clientversion=Affects 5.x versions, Fixed in kubernetes-client v5.0.3 and above.

Published CVSS scores

6.7NVDCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
CWE-94Improper Control of Generation of Code
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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