Top Tools: Best log4j-scan Solutions for Security Teams

Quick Guide: Detecting log4j-scan Vulnerabilities in Your Network—

What this guide covers

This guide explains what log4j-scan is, why it matters, how to detect vulnerable systems, and practical steps to scan, verify, and mitigate vulnerabilities found. It assumes basic familiarity with system administration and network security.

What is log4j-scan?

log4j-scan refers to tools and processes that search for systems running vulnerable versions of Apache Log4j (notably the CVE-2021-44228 and related issues) or applications exposing JNDI lookups that can be exploited. The goal is to locate instances where untrusted input can trigger remote code execution via Log4j’s lookup functionality.

Why it matters

• High severity: Exploits like CVE-2021-44228 allow unauthenticated remote code execution.
• Broad impact: Many Java applications and third-party services use Log4j, increasing attack surface.
• Active exploitation: Automated scans and exploitation attempts continue to appear in the wild; quick detection reduces risk.

Pre-scan planning

1. Inventory assets: list hosts, services, and applications running Java.
2. Obtain authorization: ensure you have written permission to scan networks and hosts. Unauthorized scanning can be illegal.
3. Choose tools: select scanning tools that match your environment (open-source, commercial, or custom).
4. Schedule and notify: perform scans during maintenance windows if scanning may affect performance. Notify stakeholders.

Popular scanning approaches

• Network-level scans: probe hosts for open services (HTTP, LDAP, RMI) and attempt exploit-style payloads to elicit identifiable responses.
• Application-layer scans: send crafted HTTP headers or parameters containing test payloads to web apps and analyze responses or callback behavior (DNS/HTTP interactions to an external monitoring service).
• Passive detection: log analysis and IDS/IPS signatures to spot attempted exploitation without active probing.
• Code/package audits: search code repositories and deployed artifacts for Log4j library versions and JNDI usage.

Tools and utilities

• Open-source scanners (examples): community-built log4j scanners that send probe payloads and track callbacks.
• Network scanners: Nmap with custom NSE scripts to detect vulnerable services.
• Cloud CSP tools: cloud providers often supply vulnerability scanners and managed detection.
  Choose tools that allow non-destructive checks (safe-mode) when needed.

Crafting safe test payloads

When possible, use payloads that trigger benign callbacks (DNS or HTTP) to a control domain you own, so detection relies on out-of-band interactions rather than executing code on targets. Example pattern: ${jndi:ldap://your-control-domain/identifier} — use only in environments you control and where you have permission.

Running an active scan (high-level steps)

1. Configure the scanner with your control domain and rate limits.
2. Scope targets: IP ranges, hostnames, or application URLs.
3. Start with a non-invasive mode or low-frequency probes.
4. Monitor application logs, network traffic, and your control-domain callbacks for indicators.
5. Triage findings: verify each positive before treating as exploitable.

Verifying findings

• Confirm the application logs show the injected payload.
• Validate external callbacks reached your control domain with the expected identifier.
• Reproduce in a test environment when possible to avoid false positives.

Mitigation steps

• Upgrade Log4j to a patched version (for CVE-2021-44228 and related: update to the latest recommended release).
• Apply configuration mitigations: remove JndiLookup class from log4j-core if immediate upgrade isn’t possible.
• Implement WAF rules and input validation to block suspicious JNDI payloads.
• Network controls: restrict outbound LDAP/RMI/other protocols from application hosts.
• Monitor logs and IDS for evidence of exploitation.

Post-scan actions

• Patch and retest affected systems.
• Document findings, remediation steps, and timelines.
• Notify stakeholders and, if necessary, customers or regulators per disclosure requirements.
• Add Log4j presence checks into regular asset-management and CI/CD pipelines.

Quick checklist

• Inventory Java apps and Log4j versions.
• Get written authorization for scanning.
• Use non-destructive probe methods first.
• Verify positives via logs or out-of-band callbacks.
• Patch or apply mitigations promptly.
• Re-scan after remediation.

Further reading and resources

Look for vendor advisories, CVE details, and trusted security community write-ups for the latest mitigations and scanner updates.