Manual:$wgMinUploadChunkSize

Files and file uploads: $wgMinUploadChunkSize
Minimum upload chunk size, in bytes.
Introduced in version:1.25.3 (Gerrit change 246885; git #59b627b0)
Removed in version:still in use
Allowed values:(integer)
Default value:1024 (1KB)

Details edit

When using chunked upload, non-final chunks smaller than this will be rejected. May be reduced based on the upload_max_filesize or post_max_size PHP settings.

This setting was introduced in a security release in MediaWiki versions 1.25.3, 1.24.4 and 1.23.11 reported in task T91203 and task T91205.