Older versions of the popular WordPress Plugin All in One SEO contains a vulnerability that allows an attacker to store malicious code in the admin panel that could potentially help them take over the administration of the website.
This plug-in (All in One SEO) helps page managers improve SEO (Search Engine Optimization) with too many settings.
One of these settings is called Bot Blocker and allows administrators to decide which machine search allowed to access their website. This setting is disabled by default, so there is no need to worry for plugin users.
Now that someone is using this feature, according to security researcher David Vaartjes, the plugin records these bots visits without clearing the text in the User Agent.
So if an attacker can change these characteristics by attaching malicious code, (if of course it knows which bot is blocked on the site) then the attack is successful.
Although too many parameters will have to match for the attack to complete successfully, don't wait, upgrade to the next version...