CVE-2021-31819Network attack vector

Remote code execution via shared serializer state

Published Sep 22, 2021 · Updated Aug 3, 2024

Remote code execution in Octopus Deploy Halibut before 4.4.7 allows remote attackers to execute code through a trusted RPC connection. MessageSerializer reuses one Json.NET serializer while decoding BSON messages, causing operation-specific contract-resolver state to interfere across concurrent reads and writes. Exploitation requires a peer whose certificate is already trusted and grants code execution in the process that hosts the communication library.

CVSS severity9.8
Critical
EPSS probability2.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Remote code execution in Octopus Deploy Halibut before 4.4.7 allows remote attackers to execute code through a trusted RPC connection. MessageSerializer reuses one Json.NET serializer while decoding BSON messages, causing operation-specific contract-resolver state to interfere across concurrent reads and writes. Exploitation requires a peer whose certificate is already trusted and grants code execution in the process that hosts the communication library.

The record

CVE
CVE-2021-31819
Published
Sep 22, 2021
Updated
Aug 3, 2024
Vendor
Octopus Deploy
Product
Halibut
Classifications
CWE-502, T1210
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 22, 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 <4.4.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Octopus Deploy · Halibutversion=unspecified <4.4.7

Published CVSS scores

9.8GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/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 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
T1210Exploitation of Remote Services

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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