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MAC ERROR after migrate to 2026 #1853
Description
Upgrading 2025 to 2026 throw MAC error,
The stack trace vs 2025
--- v2026
2026.0.0.1 default -> SshConnectionException: MAC error | kex=mlkem768x25519-sha256
app login xxx@xxx -> SshConnectionException: MAC error | kex=mlkem768x25519-sha256 cipher=aes128-ctr mac=hmac-sha2-256 | key=ssh-rsa
--- v2025
2025.1.0.1 default -> OK auth step
app login xxx@xxx -> OK, logged in answered through the tunnel (64 bytes) | kex=mlkem768x25519-sha256 cipher=aes128-ctr mac=hmac-sha2-256
--- v2026
2026.0.0.1 default -> SshConnectionException: MAC error | kex=mlkem768x25519-sha256
app login xxx@xxx -> SshConnectionException: MAC error | kex=mlkem768x25519-sha256 cipher=aes128-ctr mac=hmac-sha2-256 | key=ssh-rsa
--- v2025
2025.1.0.1 default -> OK auth step
app login xxx@xxx -> OK, logged in answered through the tunnel (64 bytes) | kex=mlkem768x25519-sha256 cipher=aes128-ctr mac=hmac-sha2-256
Activity
stegl83 commentedon Oct 27, 2026
I have the same problem.
It seems to be related to the execution environment.
App on WinServer 2019 / .NET 4.7.2 -> MAC error
App on Win 11 Pro / .NET 4.7.2 -> works fine
App on Windows Server 2025 Standard / .NET 4.7.2 (maybe using 4.8 instead) -> works fine
@iansaviour what OS are you using?
iansaviour commentedon Oct 27, 2026
@stegl83 Win 11 Home. using .NET 4.8
I using 2025.1.0.1 version again now and its work fine. I hope its checked and fixed soon so i can move to 2026.
Rob-Hague commentedon Oct 27, 2026
This is #1829 which is fixed for the next release. You can try it via https://github.com/sshnet/SSH.NET#using-pre-release-nuget-packages