In his latest post Pádraic Bradyhas posted a response to a recent post stating that in issue in Composer where the wrong package could be installed is not a security issue. Pádraic disagrees, here's why:

The problem here is quite simple. A user defines a composer.json file that requires the package bloggs/framework. Someone else creates a package on Packagist.org called evil/framework whose own composer.json states that it replaces bloggs/framework. Next, a group of poor random victims, potentially thousands, use composer to install applications with a dependency on bloggs/framework. Composer does some internal wizardry and installs evil/framework when certain conditions are met. The victims didn’t request evil/framework but they get it anyway.

He suggests that this is a kind of remote file inclusion and possibly a remote code execution vulnerabilities. He points out that the manual steps suggested in the post aren't listed in the Composer documentation and fixes for it are still pending work.

Saying one thing, but acting like it’s the other thing you don’t want people to call it, makes me think it really is the other thing. Probably because it is. Users can fall victim to a replace and it’s called “unintuitive”, but if a package states that it replaces something that might lead to the unintuitive behaviour, it’s an abuse.