A validation issue was addressed with improved input sanitization. This issue is fixed in iOS 15.3 and iPadOS 15.3, watchOS 8.4, tvOS 15.3, Safari 15.3, macOS Monterey 12.2. Processing a maliciously crafted mail message may lead to running arbitrary javascript.
https://support.apple.com/en-us/HT213256
https://support.apple.com/en-us/102770
https://support.apple.com/en-us/103177
https://support.apple.com/en-us/103176
https://support.apple.com/en-us/103175