Security Advisory 2021-10

Summary Remote Code Execution in Octopus Tentacle (CVE-2021-31819)
Advisory Number 2021-10
Discovery Date 21 Jul 2021
Patch Release Date 17 Sep 2021
Advisory Release Date 22 Sep 2021
Product Octopus Tentacle
Operating System Linux and Windows
Severity High
CVE ID CVE-2021-31819

Customers who have downloaded and installed any of the Octopus Tentacle versions listed below ("Details") are affected.

Please upgrade your Octopus Tentacle immediately to fix this vulnerability.

Customers who have upgraded Octopus Tentacle to version 6.1.938 or higher are not affected.


Octopus Deploy has given this vulnerability a high rating. This rating was given according to the Octopus Deploy severity levels, which ranks vulnerabilities as critical, high, medium, or low severity.

This is our assessment and you should evaluate its applicability to your own environment.


Octopus Tentacle uses Halibut as its communication framework. There was a deserialisation vulnerability discovered in Halibut which could allow remote code execution on Octopus Server from a trusted tentacle.

All versions of Octopus Tentacle are affected by this vulnerability.


To address this vulnerability, we have released Octopus Tentacle version:

  • 6.1.938

The latest versions of Octopus Deploy products can be downloaded from and previous versions can be downloaded from

What You Need to Do

Octopus Deploy recommends that you upgrade to the latest version (6.1.938). You can download the latest version of Octopus Tentacle from

If you can't upgrade to the latest version (6.1.938):

If you have feature version... ...then upgrade to this version
3.x or greater 6.1.938

For Octopus Tentacle versions before 3.x please contact our support team ( ) for advice on upgrading to the latest version.


There is no known mitigation for CVE-2021-31819, it is important to upgrade to a fixed version as soon as possible.


If you have any questions or concerns regarding this advisory, please contact our support team

Exploitation and Public Announcements

The Octopus Deploy security team is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.