Tashanna let me know that T-Mobile UK has officially released OS 18.104.22.1685 for the 8520. This looks like the latest release out there and even this version does not fix the security bug in the browser.
Please confirm in the comments if this works for you. Remember to click the Free Download Area button and follow through the menu tree.
NOTE: Don’t forget to delete the vendor.xml file located in c:program files>common files>research in motion>apploader to install it on a different carriers device.