In fact an incorrect implementation of CBC mode famously caused a vulnerability in Microsoft's ASP.NET in 2010 (https://learn.microsoft.com/en-us/security-updates/securityb...). The margin for error is small and even subtle mistakes or incorrect design can cripple security. Even Microsoft got it wrong once (although they handled remediation very well).
Never implement your own cryptography.
Edit:
In fact an incorrect implementation of CBC mode famously caused a vulnerability in Microsoft's ASP.NET in 2010 (https://learn.microsoft.com/en-us/security-updates/securityb...). The margin for error is small and even subtle mistakes or incorrect design can cripple security. Even Microsoft got it wrong once (although they handled remediation very well).