Certificate used to sign older Apple software expiring on October 24, 2019

On February 10, 2015, a number of Mac admins noticed that Apple was re-issuing a number of software updates. The updates themselves hadn’t changed, but were being reposted.

Apple, why are you reposting old updates with new codes. Nothing's changed, they're identical… pic.twitter.com/XMHbY798LT

— Hannes Juutilainen (@hjuutilainen) February 10, 2015

The reason was because part of the chain of certificates Apple was using to sign installers used by Apple’s software updates was expiring on February 14th, 2015.

The new expiration date was set as October 24, 2019 at 1:27 PM US Eastern Daylight Time, which is eight days from the date of this post.

Time marches on and once again, Apple is re-signing and re-issuing updates ahead of the October 24th 2019 expiration date.

Am I nuts or was Mavericks Developer Preview Recovery Update released in software update catalog yesterday? Other odd updates released recently too. #macadmins

— Kyle Crawford (@kcrawford) October 15, 2019

It looks like the re-signed installers have an expiration date of April 14th, 2029 at 5:28 PM US Eastern Daylight Time.

The certificate expiration will also affect macOS installers or boot media that are signed with the certificates which expire on October 24th. In testing by @neilmartin83, these installers will not work properly following the certificate expiration.

#MacAdmins if you have any archived macOS installers and generated boot media, it’s all gonna break on the 24th. Apple’s certs used to sign the packages are expiring. I fast-forwarded a test Mac in time to try them. Here’s what you’ll see: pic.twitter.com/DwRQw9qYbX

— Neil Martin (@neilmartin83) October 16, 2019

Apple will also be re-signing these installers though, so the fix in most cases will be to download new copies of the relevant macOS installers from the Mac App Store or Software Update.