Apache Log4j2 DoS via Self-Referential Lookup Recursion

This repository is a defensive Log4Shell lab rather than a standalone offensive exploit drop, but it does contain working exploit components. The structure combines: (1) a vulnerable target container (`log4shell-app`, based on a public Spring Boot Log4j 2.14.1 image), (2) an nginx reverse proxy with the Coraza WAF and OWASP CRS plus custom Log4Shell rules, (3) an attacker container that builds and packages multiple JNDI exploitation toolkits, and (4) Suricata/Wazuh monitoring for network and SIEM visibility. The main exploit capability lives under `attacker/`. `attacker/exploit-classes/Exploit.java` is a malicious Java class intended to be loaded through a JNDI/LDAP reference. Its static initializer executes immediately on class load and performs proof-of-exploitation actions: OS-specific command execution to write a marker file, creation of `/tmp/log4shell-exploited.txt`, and an optional reverse shell routine that connects to `172.20.0.2:4444`. There is also a stubbed environment-information collection method. This makes the repo more than a detector: it includes an actual RCE payload class. `attacker/scripts/start-ldap-server.sh` operationalizes exploitation by launching one of three JNDI infrastructures: marshalsec, JNDI-Exploit-Kit, or rogue-jndi. These are configured to serve the malicious class or execute simple commands/callbacks. `attacker/scripts/test-payloads.sh` is a payload spray/test harness that sends many Log4Shell payload variants to the nginx proxy using common injection points such as `User-Agent` and `X-Forwarded-For`. It includes LDAP, RMI, DNS, nested-expression, env/sys fallback, Unicode, whitespace, and colon-dash obfuscation variants. This script is primarily for validation of WAF/IDS coverage, but it also demonstrates realistic attack strings. The rest of the repository is focused on detection and containment. `coraza/config/log4shell-rules.conf` defines custom Coraza rules for standard and obfuscated JNDI patterns, alternate protocols, JSON/XML body inspection, and anomaly-score blocking. `nginx/` contains a multi-stage Docker build that compiles libcoraza and the coraza-nginx module, installs OWASP CRS, and exposes HTTP/HTTPS reverse proxying to the vulnerable app. `suricata/rules/log4shell.rules` adds network signatures for inbound JNDI payloads and outbound LDAP/RMI/DNS/HTTP callbacks that would indicate successful exploitation. Overall purpose: provide an isolated lab to demonstrate the full Log4Shell attack chain and, more importantly, how nginx+Coraza and Suricata can detect/block it. Because the repository includes a real malicious Java payload and scripts to stand up LDAP/JNDI exploit servers, it should be classified as a valid exploit-capable lab with operational payloads, not merely documentation or a pure detection script.

This repository is a minimal proof-of-concept payload set for CVE-2021-45105 affecting Apache Log4j 2. It does not contain executable exploit code, scripts, or framework integration; instead it consists of five text files containing progressively larger recursive lookup expressions intended to be copied into attacker-controlled input that will later be logged by a vulnerable application. The file naming convention reflects payload depth/size: 1, 10, 100, 1000, and 10000 nested expansions. There are no outbound network calls, hardcoded URLs, IPs, domains, filesystem targets, or registry paths in the repository. The exploit capability is denial of service only: if one of these strings is processed by a vulnerable Log4j instance, recursive evaluation can trigger stack exhaustion or similar failure. Structurally, the repository is just a payload corpus for testing or demonstrating the vulnerability severity at different recursion depths.