## TL;DR

https://github.com/minio/minio/issues/20319: Issue minio/minio#20319 (closed, 18 comments): When POSTing with a presigned URL to Minio, I am unable to cause the upload to fail via specifying a known bad Content-MD5 field and header.

## Steps

1. https://github.com/minio/minio/issues/20319: Issue minio/minio#20319 (closed, 18 comments): When POSTing with a presigned URL to Minio, I am unable to cause the upload to fail via specifying a known bad Content-MD5 field and header.

## When to use

You are seeing this: MinIO does not validate the Content-MD5 header or field on presigned POST uploads, so a known-bad checksum will not fail the upload. Use this skill when you run into "`Content-MD5` field/header seems to have no effect with a presigned POST url".

## When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

## Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

## Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

## Sources

- https://github.com/minio/minio/issues/20319: