Base64 String decoding

[NUnitTester]

Description

the following Code was used:
string base64String = ...;
Convert.FromBase64String(base64String);

"asdfghw=" ok, Result: < 106, 199, 95, 130, 28 >
"asdfghw=asdfghw=" ok, Exception
"asdfghw==" wrong! Should be Exception, but gives a total wrong result with less Bytes than the first one. Result: < 106, 199, 95, 135 >

.NET 4.8
Windows 10
x64, x86

. NET 3.1 Core
"asdfghw=="
System.FormatException: "The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters."

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[EgorBo]

asdfghw== is not a correct base64, it should be asdfghw=, .NET doesn't accept malformed base64 strings since .NET Core 2.1

[GrabYourPitchforks]

.NET doesn't accept malformed base64 strings since .NET Core 2.1

To be fair, we do accept some malformed strings. For instance, Convert.FromBase64String("asdfghW=") doesn't throw an exception, even though it probably should.

[buyaa-n]

asdfghw== is not a correct base64, it should be asdfghw=, .NET doesn't accept malformed base64 strings since .NET Core 2.1

As mentioned its not reproducible in Core

To be fair, we do accept some malformed strings. For instance, Convert.FromBase64String("asdfghW=") doesn't throw an exception, even though it probably should.

Resolved with #105262, closing