This is a final call for comments on https://phabricator.wikimedia.org/T161647, "Deprecate using PHP serialization inside MediaWiki".

This RFC has seen quite a bit of discussion on Phabricator, but has not been discussed in an IRC meeting. ArchCom feels that the discussion was already quite fruitful, and only minor issues are left to resolve. It was agreed that the RFC be put on Final Call: if no new concerns are raised and remain open by May 10, the RFC will be approved for implementation.

The RFC in full:

Problem statement

PHP unserialize() and serialize() can execute code when given malicious input. In most cases this serialization format is unnecessary. As a hardening measure against making a mistake that could result in remote code execution, we should avoid this format. Proposed guideline

This RFC proposes the following:

* New code SHOULD use JSON instead of PHP serialization whenever possible. * Serialization of primitive values and key-value structures MUST never use PHP serialization. * Any edge cases that require use of serialize or unserialize complicated classes, MUST protect the serialized blob with HMAC (e.g. keyed to $wgSecretKey) to protect against malicious modifications of the blob.

In addition to the new guideline for new code, this RFC proposes that we start to (slowly) convert existing uses of PHP serialization. Most likely by using JSON. The eventual goal being to remove all legacy uses of php unserialize()

Good first candidates for conversion:

* LocalisationCache * MediaHandler metadata.

The php serialization output format of the API is outside of the scope of this RFC, since we never ingest it.