Update now! Popular WordPress plugins have password bypass flaws

Researchers have discovered password bypass vulnerabilities affecting two WordPress plugins from a publisher called Revmakx.

The first vulnerable plugin is RevMakx’s InfiniteWP Client, a tool that allows admins to manage multiple WordPress sites from the same interface.

The second is WP Time Capsule, a site backup and staging tool.

The urgency is the number of sites using these tools – between 300,000 and 500,000 for InfiniteWP, and 20,000 or more for WP Time Capsule – so if you have either of these plugins, patch as soon as possible.

According to security company WebARX, who reported the vulnerabilities 7 January 2020, both bugs make it possible for attackers to login to admin accounts without a password.

The InfiniteWP bypass was found in the iwp_mmb_set_request function, used to check whether the user is attempting an authorised action.

Two actions that do that are readd_site and add_site, but neither implements an authorisation check which means that an attacker can craft a malicious request:

All we need to know is the username of an administrator on the site. After the request has been sent, you will automatically be logged in as the user.

An even simpler logic error in WP Time Capsule produces a similar result – this time, all you need to do is include the text string IWP_JSON_PREFIX in the request submitted to the WordPress server.

What to do

The good news is the developer patched the issue within a day of being told of it, although many of the sites using InfiniteWP have yet to implement the update.

For InfiniteWP, the version that fixes the flaw is v1.9.4.5, which means all versions up to and including v1.9.4.4 are vulnerable.

For WP Time Capsule, the fix is in v1.21.16, with all versions up to and including v1.21.15 being vulnerable.

Updating is most easily achieved from the Plugins tab in the WordPress dashboard. There you can see which plugins have updates available, after which it’s a matter of hitting Update now to install the new versions.

Advice for managing WordPress plugins:

• Minimise the number of plugins you have. Always remove plugins if you aren’t using them anymore. Keep your attack surface area as small as you can.
• Keep your plugins up to date. Blogging software such as WordPress can keep itself updated, but you need to keep track of the plugins yourself.
• Get rid of plugins that aren’t getting any more love and attention from their developers. Don’t stick with ‘abandonware’ plugins, because they’ll never get security fixes.
• Learn what to look for in your logs. Know where to go to look for a record of what your web server, your blogging software and your plugins have been up to. Attacks often stand out clearly and early if you know what to look for, and if you do so regularly.