Adversaries may establish persistence by executing malicious content triggered by the execution of tainted binaries. Mach-O binaries have a series of headers that are used to perform certain operations when a binary is loaded. The LC_LOAD_DYLIB header in a Mach-O binary tells macOS and OS X which dynamic libraries (dylibs) to load during execution time. These can be added ad-hoc to the compiled binary as long as adjustments are made to the rest of the fields and dependencies.(Citation: Writing Bad Malware for OSX) There are tools available to perform these changes.

Adversaries may modify Mach-O binary headers to load and execute malicious dylibs every time the binary is executed. Although any changes will invalidate digital signatures on binaries because the binary is being modified, this can be remediated by simply removing the LC_CODE_SIGNATURE command from the binary so that the signature isn’t checked at load time.(Citation: Malware Persistence on OS X)
LC_LOAD_DYLIB Addition
source_name: mitre-attack  url: https://attack.mitre.org/techniques/T1546/006  external_id: T1546.006     source_name: Malware Persistence on OS X  description: Patrick Wardle. (2015). Malware Persistence on OS X Yosemite. Retrieved July 10, 2017.  url: https://www.virusbulletin.com/uploads/pdf/conference/vb2014/VB2014-Wardle.pdf     source_name: Writing Bad Malware for OSX  description: Patrick Wardle. (2015). Writing Bad @$$ Malware for OS X. Retrieved July 10, 2017.  url: https://www.blackhat.com/docs/us-15/materials/us-15-Wardle-Writing-Bad-A-Malware-For-OS-X.pdf     