Security Advisory 2025-07

Summary .NET Security Feature Bypass Vulnerability
Advisory Number 2025-07
Discovery Date 14 OCT 2025
Patch Release Date 15 OCT 2025
Advisory Release Date 21 OCT 2025
Product Octopus Server
Operating System Windows and Linux
Severity Critical
CVE ID CVE-2025-55315 (Microsoft)

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

Please upgrade your Octopus Server immediately to fix this vulnerability.

Customers who have upgraded Octopus Server to version 2025.3.14372 or higher are not affected. As of the 21 OCT 2025 Octopus Server version 2025.4.x is only available on Octopus Cloud. Octopus Cloud customers do not need to take any further action as all instances have been updated to the patched version (2025.4.4740)

Severity

Octopus Deploy has given this vulnerability a critical 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.

Details

Microsoft has disclosed a critical vulnerability (CVE-2025-55315, CVSS 9.9) affecting the .NET stack used by your Octopus Deploy Cloud Instance or Octopus Server installation. While there is no known active exploitation or public exploit code we have immediately released updated versions with the patched dependency.

This security flaw could potentially allow authenticated attackers to hijack sessions or cause system disruptions.

Our team has prepared and tested releases with the necessary security patches.

Reference: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-55315

Fix

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

  • 2025.2.13166
  • 2025.3.14372
  • 2025.4.4740

The latest versions of Octopus Deploy products can be downloaded from https://octopus.com/downloads and previous versions can be downloaded from https://octopus.com/downloads/previous

What You Need to Do

Octopus Deploy recommends that you upgrade to the latest version (2025.3.14372). You can download the latest version of Octopus Server from https://octopus.com/downloads

If you can't upgrade to the latest version (2025.3.14372):

If you have feature version... ...then upgrade to this version
2025.2.x and older 2025.2.13166
2025.3.x 2025.3.14372
2025.4.x 2025.4.4740

Mitigation

There is no known mitigation for CVE-2025-55315, it is important to upgrade to a fixed version as soon as possible.

Support

If you have any questions or concerns regarding this advisory, please contact our support team https://octopus.com/support.

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 at the time of publishing.

Source

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-55315