Security Advisory 2021-02

Summary Local privilege escalation in Octopus Tentacle (CVE-2021-26557)
Advisory Number 2021-02
Discovery Date 01 Jan 2021
Patch Release Date 07 Mar 2021
Advisory Release Date 10 Mar 2021
Product Octopus Tentacle
Operating System Windows
Severity High
CVE ID CVE-2021-26557

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 using Octopus Cloud are not affected.

Customers who have upgraded Octopus Tentacle to version 6.0.489 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.


When Octopus Tentacle is installed using a custom folder location, folder ACLs are not set correctly and could lead to an unprivileged user using DLL side-loading to gain privileged access.

All versions of Octopus Tentacle are affected by this vulnerability.


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

  • 6.0.489

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 (6.0.489). You can download the latest version of Octopus Tentacle from

If you can't upgrade to the latest version (6.0.489):

If you have feature version... ...then upgrade to this version
3.x or greater 6.0.489

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


If you are unable to patch your Octopus Tentacle installation you can effectively mitigate this vulnerability by removing any “CreateFiles” or “AppendData” permissions for “BUILTIN\Users” on the Octopus Tentacle installation directory.

The following links are for the PowerShell commands that can be used to check folder ACLs and update them:


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 malicious use of the vulnerability that is described in this advisory.


This vulnerability was found by Octopus Deploy Engineering.