CVE-2021-4118

Code execution via unsafe YAML hyperparameter loading

Published Dec 23, 2021 · Updated Aug 3, 2024

Deserialization in PyTorch Lightning before 1.6 allows local users to execute code by supplying a crafted YAML hyperparameter file. The load_hparams_from_yaml function passes the opened configuration file to yaml.load with UnsafeLoader, permitting Python object construction from YAML content. A user or workflow must load an attacker-controlled hyperparameter file, and resulting code runs with the consuming process's permissions.

CVSS severity7.8
High
EPSS probability0.98%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Deserialization in PyTorch Lightning before 1.6 allows local users to execute code by supplying a crafted YAML hyperparameter file. The load_hparams_from_yaml function passes the opened configuration file to yaml.load with UnsafeLoader, permitting Python object construction from YAML content. A user or workflow must load an attacker-controlled hyperparameter file, and resulting code runs with the consuming process's permissions.

The record

CVE
CVE-2021-4118
Published
Dec 23, 2021
Updated
Aug 3, 2024
Vendor
Lightning AI
Product
PyTorch Lightning
Classifications
CWE-502, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 23, 2021CVE 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=unspecified <1.6

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Lightning AI · PyTorch Lightningversion=unspecified <1.6

Published CVSS scores

7.8huntr.devCVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
T1204.002Malicious File

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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