The latest flaw - which can cause an iPhone to crash and even restart - was tweeted by Abraham Masri, and his code was uploaded to programming site GitHub.
Sending a message containing the software developer's code would be enough to activate the bug, which also makes the Safari browser crash on Mac, as well as causing other slowdowns.
Mr. Masri - who said he "always reports bugs" before releasing them - later removed his code from GitHub.
He explained: "I'm not going to re-upload it... I made my point. Apple needs to take such bugs more seriously."
Users don't need to worry about the flaw, though, with security expert Graham Cluley explaining it's more annoying than it is dangerous.
He wrote on his blog: "Something about the so-called ChaiOS bug's code gives your Apple device a brainstorm.
"Ashamed about the mess it gets itself in, Messages decides the least embarrassing thing to do is to crash.
"Nasty. But, thankfully, more of a nuisance than something that will lead to data being stolen from your computer or a malicious hacker being able to access your files. (sic)"