As usual, the company provided sparse details about the flaw, though it said it was aware of the issue being exploited in the wild.
The issue was described as a type confusion issue in XNU. iOS 13 ow now officially not supported by Apple.
The lack of detail was explained in this sentence: "For our customers' protection, Apple doesn't disclose, discuss, or confirm security issues until an investigation has occurred and patches or releases are available."
Google researchers Erye Hernandez, Clément Lecigne and Ian Beer were credited with finding the flaw.
This flaw took to 16 the number of zero-day flaws that have been reported in Apple's products this year.
Google will release details of the flaw after 30 days, as per its official policy.
Contacted for comment, Satnam Narang, staff research engineer at security outfit Tenable, said: "The latest zero-day flaw, identified as CVE-2021-30869, was discovered by researchers at Google Threat Analysis Group and Google Project Zero.
"Details about the vulnerability will remain under wraps for at least 30 days by Google to allow for users to apply the newly available patches. However, it appears that CVE-2021-30869 was used as part of a vulnerability chain with a remote code execution flaw in WebKit.
"Zero-day vulnerabilities are valuable for any attacker, but they are often mostly used by advanced persistent threat (APT) actors that have a limited set of targets.
"While there are other more impactful vulnerabilities that users should prioritise, on a basic level, it is almost always a win to apply patches in a timely manner to ensure devices are protected."