Tuesday, 16 January 2018

Sensible Targets

Fig 1. Current release cycle graph
There has been a lot of talk recently about which versions of PHP you should support for your new projects or packages.

As a release manager for PHP, someone who watches the way releases evolve extremely closely, and has some sway over what gets fixed and what doesn't, and as someone who helped to draft the security classification document for PHP; I feel I have some useful things to say on this subject, so here goes ...

The Release Cycle

Every release of PHP goes through the following cycle:

Pre Release:
  • 3 Alpha, two weeks apart
  • 3 Beta, two weeks apart
  • 6 RC, two weeks apart
Release:
  • GA, roughly 6 months after the first alpha
Actively Supported:
  • For two years the PHP team make a patch release every month with bug and security fixes.
Security Only:
  • For the final year of the three year cycle, the PHP team will make a patch release when security fixes warrant a release.

What isn't a security issue ?

We have various definitions to classify the threat level posed by any security issue, but importantly for the community at large, we also have a definition of what is not a security issue:
  • requires invocation of specific code, which may be valid but is obviously malicious
  • requires invocation of functions with specific arguments, which may be valid but are obviously malicious
  • requires specific actions to be performed on the server, which are not commonly performed, or are not commonly permissible for the user (uid) executing PHP
  • requires privileges superior to that of the user (uid) executing PHP
  • requires the use of debugging facilities - ex. xdebug, var_dump
  • requires the use of settings not recommended for production - ex. error reporting to output
  • requires the use of non-standard environment variables - ex. USE_ZEND_ALLOC
  • requires the use of non-standard builds - ex. obscure embedded platform, not commonly used compiler
  • requires the use of code or settings known to be insecure
Any issue that falls under any of the above categories, even though it may have security implications for you personally, is not treated as a security issue. It may be fixed as a normal bug, but that fix will not be included in a security fix only release.

In addition, any security issue classified as having a low threat level will not necessarily be included in a security fix only release. The lowest level of threat is defined thus:
This issue allows theoretical compromise of security, but practical attack is usually impossible or extremely hard due to common practices or limitations that are virtually always present or imposed.
This also includes problems with configuration, documentation, and other non-code parts of the PHP project that may mislead users, or cause them to make their system, or their code less secure.
Issues that can trigger unauthorised actions that do not seem to be useful for any practical attack can also be categorised as low severity.
Security issues, that are present only in unstable branches, belong to this category, too. Any branch that has no stable release, is per se not intended for the production use.
Aside from those bugs which may or may not be a security issue, there is a variety of bugs that are definitely not a security issue, but may cause your project serious harm, or present serious problems for your package - No fix is forthcoming for these, the vast majority of bugs, while the release is in security fix only cycle.

What should I target ?

Targeting a security fix only release of PHP for new projects doesn't make any sense: When a release is in security fix only cycle you should be concentrating on getting old projects upgraded, and a year is plenty of time to do that. In the case of PHP 5.6, we extended the security cycle to two years. If you are reading this and thinking a year isn't long enough to do that, then there is something wrong with the way you deploy or support projects or packages: It has to be long enough, running a version of PHP without active support is dangerous for your business, reputation, and soul.

New projects or packages should obviously target an actively developed version of PHP. At the time of writing both 7.1 and 7.2 are being actively developed (there will always be two versions in active development). Whether you choose to use 7.1 or 7.2 depends on your project or package, perhaps you'd like to use some new features, and not have to worry about security cycle for nearly two years and so can reasonably target 7.2. Perhaps you have reasons to stick with 7.1, and are prepared to deal with security cycle before the year is out.

The bottom line is this: New projects or packages must target an actively developed, fully supported version of PHP.

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