Downgrading CDMA iPhone 4 firmware 4.2.10 > 4.2.8 trials and tribulations

[Daman09]

Hello all, I have been an avid jailbreaker and iPhone user for two years, and nothing has stumped me as much as what I have been trying to do for the past week.

Back-story: My girlfriend got an iPhone 4 back in April, finally decided she wanted to get her phone jailbroken a few weeks ago, and had me do it on firmware 4.2.8. Everything works well, I make sure the SHSH blobs are saved and all that good stuff. A week ago, the new firmware 4.2.10 comes out, making an untethered jailbreak currently impossible when on it. I guess I never told my girlfriend to not update the firmware, so, she does, and after having gotten use to the convenience of apps such as BiteSMS and SBSettings, finds her unjailbroken phone inefficient. Fortunately, I tell her I can downgrade her phone from 4.2.10 to 4.2.8, because I have saved the SHSH blobs.
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Not so Fast: So, being as such that I have only ever downgraded my phone once about a year ago on a 3GS, I investigate how to downgrade her phone. I go to Redmond Pie and this guide is essentially what I want, knowing that the fimwares mentioned have CDMA equivalents. So, I follow that guide to the letter it looks like it installs on the iPhone, then get an error, iPhone shows connect to itunes screen. No problem, the guide mentioned this, Tiny Umbrella exit recovery will work.

It doesn't, boots right back to that connect to itunes icon, I put it in DFU mode, and try fix recovery, now I'm looking at a screen that says green pois0n at the top, with a few lines, one of them saying "Unable to find fs_unmount". At this point I figure I have done something wrong, and retry the entire thing, same thing. I have gotten to the point where I have used tiny umbrella as the TSS server instead of the cydia server, used redsn0w and greenpois0n with it in DFU mode, tried doing incremental downgrades down to 4.2.9 then 4.2.8 (4.2.9 did the same exact thing).

I do a bunch of research and eventually find this, which essentially says on newer iDevices, when trying to downgrade, the baseband causes the device to panic during the downgrade process. I go back and try to downgrade again, and realize the progress bar on the iPhone gets to about 75% before it going to the connect to iTunes screen. Perhaps this is the problem?

After finding that I notice that after the 75% downgrade completion, if I were to open Tiny Umbrella, the recovered device would identify itself as being on 4.2.10 still.

I am utterly confused and have no idea what to do, but I am determined to get this device downgraded, even if it takes up the rest of my summer. Does anyone have any advice to help me downgrade this Verizon iPhone down to 4.2.8 from 4.2.10? Any and all advice would be appreciated.

[iYeow]

You can't because apple is no longer signing the 4.2.8 baseband anymore. But you could if you have 4.2.6 shsh blob.

[i.Annie]

Custom 4.2.8 firmware?

[iYeow]

Is it possible ?

[Daman09]

That's unfortunate, why was a larger fuss not made about this inability to downgrade? And is this only for Verizon phones?

[iYeow]

The hardware itself is very different from GSM model Try custom firmware and see.

[i.Annie]

I am not sure if cfw will work or not, I just always thought it would. I mean I used a cfw to 4.2.6 but I've never tries 4.2.8. I have SHSHs for both, I just chose 4.2.6 bc I need a working iBooks

Edit: I think you really should try a custom fw though. Make one with sn0wbreeze or pwnagetool for Mac.

[Daman09]

I will make a custom firmware version, and get back to you to tell you if it works. Thanks so much, you have given me a little hope.

[i.Annie]

Cool, I'm eager to know if it will work.

Just don't forget to get into pwned dfu mode before restoring to it or you'll get error 16xx or 21 in iTunes. I myself prefer redsn0w or if you've got a Mac pwnagetool's dfu is good too. I just don't like iReb/sn0wbeeeze's dfu, never once worked for me.

[Daman09]

Cool, I'm eager to know if it will work.

Just don't forget to get into pwned dfu mode before restoring to it or you'll get error 16xx or 21 in iTunes. I myself prefer redsn0w or if you've got a Mac pwnagetool's dfu is good too. I just don't like iReb/sn0wbeeeze's dfu, never once worked for me.

So, I'm just curous, im trying to build the IPSW in Sn0wbreeze, are there any specific settings I should be checking off for this firmware that would get around the Baseband boot out? I was going to guess the hacktivate option would do that, but in my experience with such things, that is generally used for unlocking iPhones. Any suggestions? I'll be able to get my hands back on that CDMA phone tomorrow afternoon.

EDIT: Just realized that option was uncheckable, which makes sense for that verizon firmware. I guess there is really not much else I can do with the sparce settings available in Sn0wbreeze. I'll give an update tomorrow.

[Daman09]

It worked! I was forced to do it on windows though, as it seems that Pwnage tool doesn't support firmware 4.2.8 yet, it was not a problem, I used sn0wbreeze and made a custom package. I took you advice and tried to do a pwnage DFU with redsn0w, it didn't work, I pointed it to both the 4.2.8 FW, which just lead the iphone to reboot, and the 4.2.10 firmware, which RS didn't recognize. So, the iReb within Sn0wbreeze did the job effectively. I used Tiny Umbrella and effectively restored her iPhone back down to 4.2.8.

Thank you guys for the help, I don't think I could have done it without you.

[i.Annie]

Awesome now I know it can be done!

[Mysterion]

I want to downgrade my iPhone 4 to 4.2.8 too but TinyUmbrella wont show 'Start TSS Service' button.

[i.Annie]

Did you click "Save SHSHs" first?

[Mysterion]

I already saved the 4.2.8 shsh blobs before I upgraded to 4.2.10.

[Jmills87]

Yes, the easiest way to downgrade from 4.2.10 to 4.2.8 is to create a custom firmware using either Sn0wbreeze 2.7.3 or Pwnage Tool 4.2.

Since Pwnage Tool 4.2 doesn't have the 4.2.8 firmware bundle by default, you have to add the firmware bundle to the pwnage tool package. There is a tutorial below that tells/shows you how to do it:

Untethered 4.2.8 Jailbreak Verizon CDMA iPhone4 for Mac Using Pwnage Tool | iPhoneBlogr.com

[Mysterion]

I use a Windows XP computer not a Mac

[i.Annie]

Then use sn0wbreeze.

Generally regardless of whether you already saved your SHSHs or not, in TU if you click Save SHSHs usually the TSS server will be allowed to click thereafter. That's why I asked.

[Jaybell4444]

I downgraded successfully downgrading (in DFU Mode) to 4.2.6! Then I upgraded to 4.2.8 and used snowbreeze 2.7 to jailbreak it. Worked beautifully. remember that you still have to use tiny umbrella to exit recovery once you downgrade to 4.2.6!
4.2.8 not signed anymore
go with 4.2.6 stock

[iYeow]

I want to downgrade my iPhone 4 to 4.2.8 too but TinyUmbrella wont show 'Start TSS Service' button.

You have to free port 80 for tss server to run, close skype or anything that is using port 80