WordPress 5.0.1 Security Release
WordPress 5.0.1 is now available, since Wednesday night, December 12, 2018. This is a security release for all versions since WordPress 3.7. We strongly encourage you to update your sites immediately. This WordPress Security release fixes 7 vulnerabilities.
WordPress versions 5.0 and earlier are affected by the below-presented bugs, which are fixed in version 5.0.1. Updated versions of WordPress 4.9 and older releases are also available, for users who have not yet updated to 5.0.
Backwards Compatibility Breaks in WordPress 5.0.1
5.0.1 was just released to fix several security bugs. The Security team tried very hard to mitigate all of the vulnerabilities without any back-compat breaks, but unfortunately, there were a few cases where that was not possible. Security patches are backported to the 3.7 branch, so these BC breaks also apply to versions 4.9.9, 4.8.8, etc.
Unauthorized File Deletion
Karim El Ouerghemmi discovered that authors could alter metadata to delete files that they weren’t authorized to. This issue stems from the 2 arbitrary file delete vulnerabilities fixed in WordPress 4.9.6. The fix in WordPress addressed how attachment files are deleted, by restricting the file paths to the uploads directory, but did not address the issue of authors having the ability to change the attachment paths to arbitrary files. An author can use this to delete other users’ attachments.
Unauthorized Post Creation
Simon Scannell of RIPS Technologies discovered that authors could create posts of unauthorized post types with specially crafted input. The requirement that an attacker would need at least ‘author’ level privileges make the likelihood of this being exploited on a widespread basis very low.
PHP Object Injection
Sam Thomas discovered that contributors could craft metadata in a way that resulted in PHP object injection. This looks to be similar to the 2 arbitrary file delete vulnerabilities fixed in WordPress 4.9.6. This vulnerability allows an author to assign an arbitrary file path to an attachment. The file path supplied by the author uses the phar:// stream wrapper on a previously uploaded attachment which leads to object injection utilizing a “feature” of the PHAR file type which stores serialized objects in the metadata of the PHAR file. Sam Thomas presented this technique at BlackHat earlier this year.
Privilege Escalation / XSS
Tim Coen discovered that contributors could edit new comments from higher-privileged users, potentially leading to a cross-site scripting vulnerability. This is another vulnerability that requires a higher-level user role, making the likelihood of widespread exploitation quite low. WordPress addressed this issue by removing the "form" tag from their HTML whitelist.
XSS That Could Impact Some Plugins
Tim Coen also discovered that specially crafted URL inputs could lead to a cross-site scripting vulnerability in some circumstances. The code change in WordPress core affects the wpmu_admin_do_redirect function which is not used in WordPress, but a plugin may call this function somewhere.
Sensitive Data Exposure
Team Yoast discovered that the user activation screen could be indexed by search engines in some uncommon configurations, leading to exposure of email addresses, and in some rare cases, default generated passwords. WordPress has addressed this by stripping the activation key used in the URL and storing the value in a cookie instead.
Tim Coen and Slavco discovered that users with ‘author’ privileges on Apache-hosted sites could upload specifically crafted files that bypass MIME verification, leading to a cross-site scripting vulnerability. Yet again, the ‘author’ level user requirement makes an unlikely target for attackers.