shubham0d / cve-2021-30853

A sample POC to test CVE-2021-30853

CVE-2021-30853

A simple POC script to test for CVE-2021-30657 affecting MacOS.
This CVE allows bypass of gatekeeper, notraization and xprotect checks.

Vulnerability detail

This Vunlerability occurs when you don't define a interpreter( or specify a interpreter that itself is a shell script) in first line(shebang) of the main script of your executable bundle. This will cause xpcproxy to invokes posix_spawnp to launch the interpreter-less script-based application. This initially errors out (no interpreter → ENOEXEC), but then posix_spawnp "recovers" and (re)executes the script ...this time directly via /bin/sh.
Later, the AppleSystemPolicy kext intercepts the process launch to ensure its conformant (signed, notarized, etc). But it checks /bin/sh without any variable set, so execute the script without any default checks.
Based on thread: https://twitter.com/objective_see/status/1473741597368098819

Steps to reproduce

• Put your desireable shell script code in payload.sh. Keep in mind to not modify the first line of script (#!/usr/bin/command).
• Execute setup.sh.
• This will generate a bait.dmg that will contain our malicious app bundle.
• Share it to the victim through internet.
• When victim will double click on app icon after mounting dmg, it will execute the payload script without any gatekeeper's checks.

Affected version

macOS Big Sur < 11.6

Technical details

https://objective-see.com/blog/blog_0x6A.html