September 2025 Windows security updates issue

Issue

Windows Updates released in September 2025 are causing authentication failures between computers. The following updates have been identified as affected: KB5064081, KB5065426 and KB5065429.

Any Windows feature requiring computer-to-computer authentication may be affected, including:

• Network browsing between computers
• Printing to shared printers via another computer (direct printing to network printers is not affected)
• Launching Toniq on workstations if the Toniq server is impacted

Cause

It has been determined that authentication failures are occurring on networks where computers have been cloned from the same source machine.

Cloning is a method commonly used by computer hardware companies to speed up the setup process by copying a single machine’s hard drive to multiple computers with similar hardware. This approach allows IT technicians to avoid performing a full installation of Windows and its updates on each device, as the source disk already contains the necessary configuration.

However, the cloning process also copies the Computer Security ID (SID), resulting in multiple computers sharing the same SID if it is not reset before cloning. Although a process exists to remove the SID before cloning, it has often been considered unnecessary, even by companies closely associated with Microsoft.

Following the installation of the latest Windows Updates, communication between computers cloned from the same source is blocked. When two computers with identical SIDs attempt to authenticate, the process fails because each computer cannot verify the other’s identity. Essentially, each computer says, “You’re pretending to be me. I’m not going to let you in because I don’t believe that you are who you say you are.”

Resolution

It is recommended that the hardware supplier be contacted to resolve this issue, even if the current Toniq Server is not affected. The suppliers can be referred to this page as needed.

If the issue is not addressed, printing to printers attached to another computer and opening Toniq (if a cloned machine becomes the Toniq server in the future) may not be possible.

This issue is caused by a change to Windows authentication, which is a critical part of its built-in security. As a result, software such as file and printer sharing, as well as Toniq, may be affected.

• Changing the Computer SID has been identified as the most effective permanent solution.
  • Important: Before trying any utilities to change the SID, a full backup of the computer is recommended.

Hardware suppliers can use one of the following tools to change the SID:

• SIDCHG (SID changer utility) by Stratesave Systems - This tool has been used successfully in Toniq testing.
• Microsoft’s sysprep utility - this tool should be used with caution, as it may cause Microsoft Store apps to stop working and could affect built-in accounts (such as Administrator) or links to Microsoft accounts.