CVE-2021-39207Network attack vector

Code execution via unsafe YAML configuration loading

Published Sep 10, 2021 · Updated Aug 4, 2024

Unsafe YAML deserialization in Meta Platforms ParlAI before 1.1.0 allows attackers to execute code through a crafted local configuration file. The parse_configuration_file and model-chat blueprint helpers pass YAML contents to yaml.load with FullLoader or the default loader instead of SafeLoader. Exploitation requires control of a local configuration that a chat-service or crowdsourcing workflow later loads, after which code runs with that process's privileges.

CVSS severity8.4
High
EPSS probability1.79%
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 Meta Platforms ParlAI before 1.1.0 allows attackers to execute code through a crafted local configuration file. The parse_configuration_file and model-chat blueprint helpers pass YAML contents to yaml.load with FullLoader or the default loader instead of SafeLoader. Exploitation requires control of a local configuration that a chat-service or crowdsourcing workflow later loads, after which code runs with that process's privileges.

The record

CVE
CVE-2021-39207
Published
Sep 10, 2021
Updated
Aug 4, 2024
Vendor
Meta Platforms, Inc.
Product
ParlAI
Classifications
CWE-502
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 10, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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=< 1.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Meta Platforms, Inc. · ParlAIversion=< 1.1.0

Published CVSS scores

8.4GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L
8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
6.5NIST NVDAV:N/AC:L/Au:S/C:P/I:P/A:P

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)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data

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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