iOS 11 has had some interesting bugs, including one that would cause "i" to autocorrect to "A[?]" and another that'd cause the iPhone X to become unresponsive after a rapid temperature drop. Now another issue has come to light.
A link is going around that can freeze and possibly crash your iPhone. The bug is called "chaiOS" by its founder Abraham Masri, who posted the malicious link to GitHub earlier this week.
The link is to a webpage with hundreds of thousands of characters in its metadata. The issue is that because Messages generates a preview of links so you can see what you're about to click on, but it can't handle the chaiOS link.
The original chaiOS link is now gone from Masri's GitHub page, but because that page was publicly available for awhile, it's possible that others copied the link and are continuing to use it.
The chaiOS bug was tested on an iPhone X and iPhone 5s, and Masri said that it affects versions of iOS from 10.0 through 11.2.5 beta 5.
Masri reported the bug to Apple on January 15, and Apple has confirmed that it will release an update to fix the chaiOS bug next week. If you find yourself affected by the bug before then, you can try to delete the thread in Messages. If you're unable to because the phone keeps crashing, another option is to perform a factory restore on your device.