Which is the newest OS I can upgrade a 24" early 2009 iMac?

Question

Which is the newest OS I can upgrade a 24" early 2009 iMac?

Nowadays the user cannot access some https sites because "The connection is not private" or something similar depending on the browser used: ERR_CERT_DATE_INVALID despite it is valid. I can browse those sites from my Big Sur

I found that those sites have in common their certificates were issued by R3 Let's Encrypt.

letsencrypt.org/docs/certificate-compability states that macOS<10.12.1 will no longer validate their certificates as from Oct 1, 2021

So 10.12 is needed at least.

Will this iMac work okay with this OS? The user mostly uses web services, no need to run hard software.

How to upgrade?

Thank you

[Image Edited by Moderator to Remove Serial Number]

Posted on Oct 6, 2021 5:18 PM

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Answer 1

ckuan

Level 10

120,914 points

Oct 6, 2021 5:21 PM in response to Daniel Stonek

The highest macOS version that the iMac can install is OS X El Capitan 10.11.6, no further.

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Answer 2

Jack-19

Level 8

46,188 points

Oct 7, 2021 8:46 AM in response to Daniel Stonek

Sorry, there are no other fixes. OS X El Capitan is an obsolete version of macOS that will no longer be updated and may not work well with modern internet services.

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Answer 3

Niel

Community+ 2025

Level 10

741,251 points

Oct 6, 2021 5:28 PM in response to Daniel Stonek

Use another web browser. If you need to patch Safari, click here, or choose Utilities from the Finder's Go menu, open the Script Editor, and run:

do shell script "curl -k https://letsencrypt.org/certs/isrgrootx1.der > ~/Downloads/isrgrootx1.der"

Double-click the downloaded certificate.

(205859)

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Answer 4

Oct 7, 2021 8:33 AM in response to Niel

I had to run the script from Big Sur and send isrgrootx1.der to Yosemite. I installed it but things changed a bit.

There are sites that clicking on Continue in the certificate pop-up is enough to display their content.

There are others the "Continue" triggers the same pop-up. Clicking Certificate I checked "Always trust" but nothing changes.

In other sites simply "Cannot access ... privacy...". Always in Safari.

I made a call to my local Mac tech folks and they say they know the issue because they have to work with old hardware and software. With 10.11 El Capitan they found that Firefox 78.01 works good. Will install it in Yosemite and tell you what happens.

I guess there are a lot of people with old macs facing the same problem.

Could Apple take account into it and share a solution?

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Answer 5

Oct 7, 2021 9:12 AM in response to Jack-19

FF 78.01 works good in Yosemite too.

I tried other internet browsers but none of them work with OS < 10.12

The exception is Tor Browser which also works in 10.10 with its last version.

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Answer 6

Oct 8, 2021 2:29 PM in response to Niel

https://www.arqbackup.com/blog/how-to-fix-error-1202-on-mac-os-x-prior-to-10-12-1/

After opening the certificate and ... Trust... reboot I got Safari work okay in all websites

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Which is the newest OS I can upgrade a 24" early 2009 iMac?

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