Steps to reproduce:
1. Create a file with 4 bytes with the given values: 247, 178, 187, 190
You can use this Ruby script for this:
File.open("invalid.txt", "w") do |file|
file << "\xf7\xb2\xbb\xbe"
2. Execute `iconv -f UTF-8 -t UTF-8 invalid.txt`
Expected: iconv should say "cannot convert"
Actual: it works, we get the same bytes as the input (you can see this if you put the result of iconv in another file)
The first byte of value 247 is not valid in UTF-8, the maximum allowed value for it is 0xF4 (244). It seems a value bigger than that for the first byte is not valid because the maximum codepoint value of 0x10FFFF.