Apache 404 Not Found — Missing Resource Analysis

WebServerErrors Apache Reconnaissance / Scanning

What This Means

Analyze Apache 404 errors to distinguish between broken links and active vulnerability scanning. Detect automated reconnaissance and directory enumeration against your Apache server.

Example Log

198.51.100.77 - - [08/Mar/2026:16:20:33 +0000] "GET /administrator/index.php HTTP/1.1" 404 452 "-" "Mozilla/5.0"

Indicators of Suspicious Activity

404 requests for CMS admin panels that do not exist on your server
Requests for common webshell filenames (c99.php, r57.php, shell.php)
High-frequency 404 bursts from single IPs using scanning tools
Requests for .asp/.aspx pages on a pure Linux/PHP server
Sequential probing of paths from known wordlists (dirb, dirbuster)
404 requests with exploit payloads in query parameters

How to Investigate

Parse Apache access logs and group 404s by source IP and URI
Check if any URIs contain injection patterns (SQL, XSS, command injection)
Verify Googlebot claims with reverse DNS verification
Compare scanning patterns against known wordlists
Check if 404-triggering IPs also made successful requests
Review the Apache error log for additional context on 404 failures

Recommended Mitigations

Configure Apache ErrorDocument 404 to serve a custom page without server details
Deploy mod_evasive to automatically throttle high-frequency requesters
Block common scanning tool User-Agent strings using mod_rewrite
Implement fail2ban with Apache 404 monitoring rules
Deny access to file extensions not used by your application
Consider deploying a honeypot URL that alerts on access

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Related Log Types

Related Attack Patterns

Frequently Asked Questions

How do I analyze Apache 404 patterns? ▼

Use tools like GoAccess, AWStats, or grep/awk on the access log. Group 404s by source IP and URI to separate legitimate broken links from scanning activity.

How can I block scanners generating 404s in Apache? ▼

Use mod_evasive for rate-based blocking, fail2ban for log-based IP banning, and mod_rewrite rules to block known scanner User-Agent strings.

Should I redirect or block old URLs returning 404? ▼

For legitimately moved content, use 301 redirects to preserve SEO value. For scanner-generated 404s, returning a minimal 404 or blocking the IP is more appropriate.