4.5.1 had several later security patches, including:
At its launch, .NET 4.5.1 was bundled with and Windows Server 2012 R2 . It was also made available for download on Windows 7 SP1, Windows Vista SP2, and Windows Server 2008/2012. Lifecycle Status microsoft dotnet framework 4.5.1
If you’re maintaining legacy apps stuck on , the interesting review is: “It works, but upgrade to 4.8 (still supported) immediately unless you like CVEs.” 4.5.1 had several later security patches
Microsoft officially ended support for .NET Framework 4.5.1 on January 12, 2016 . including: At its launch
Would you like a comparison with 4.8 or .NET 8/9 from a migration perspective?