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Here's a kextd method exposed via MIG (com.apple.KernelExtensionServer) kern_return_t _kextmanager_unlock_kextload( mach_port_t server, mach_port_t client) { kern_return_t mig_result = KERN_FAILURE; if (gClientUID != 0) { OSKextLog(/* kext */ NULL, kOSKextLogErrorLevel | kOSKextLogIPCFlag, "Non-root kextutil doesn't need to lock/unlock."); mig_result = KERN_SUCCESS; goto finish; } if (client != (mach_port_t)dispatch_source_get_handle(_gKextutilLock)) { OSKextLog(/* kext */ NULL, kOSKextLogErrorLevel | kOSKextLogIPCFlag, "%d not used to lock for kextutil.", client); goto finish; } removeKextutilLock(); mig_result = KERN_SUCCESS; finish: // we don't need the extra send right added by MiG mach_port_deallocate(mach_task_self(), client); return mig_result; } If the client has UID 0 but passes an invalid client port this code will drop a UREF on client port then return KERN_FAILURE. Returning KERN_FAILURE in MIG means all resources will be released which will cause client to be passed to mach_port_deallocate again, even though only one UREF was taken. You'll have to use a debugger attached to kextd to see this behaviour. This class of bug is exploitable; please see the writeup for mach_portal from 2016 where I exploited a similar issue [https://bugs.chromium.org/p/project-zero/issues/detail?id=959] The TL;DR is that an attacker can drop an extra UREF on any send rights in kextd for which the attacker also has a send right; you could use this to cause a name for a privileged service to be deallocated then cause the name to be reused to name a port you control. Exploitation of this would be a privesc from unentitled root to root with com.apple.rootless.kext-management and com.apple.rootless.storage.KernelExtensionManagement entitlements, which at least last time I looked was equal to kernel code execution. tested on MacOS 10.13.2 Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/44561.zip |
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