
Analyzing Web Server Logs For Intrusion
- 314 installs
- 27.3k repo stars
- Updated August 2, 2026
- mukul975/anthropic-cybersecurity-skills
Detect and investigate suspicious activity in web server logs to identify potential intrusions or security breaches.
About
This skill teaches how to parse, search, and analyze web server logs to detect unauthorized access attempts, malicious payloads, and anomalous behavior. A solo builder uses it when investigating security incidents or implementing proactive threat monitoring on their production systems. It matters because early intrusion detection can prevent data breaches, unauthorized access, and service disruptions.
- Detect suspicious patterns in HTTP requests and access logs
- Identify common attack vectors like SQL injection and XSS attempts
- Correlate log data to investigate security incidents
Analyzing Web Server Logs For Intrusion by the numbers
- 314 all-time installs (skills.sh)
- +18 installs in the week ending Aug 4, 2026 (Skillselion tracking)
- Ranked #622 of 2,203 Security skills by installs in the Skillselion catalog
- Security screen: HIGH risk (skills.sh audit)
- Data as of Aug 5, 2026 (Skillselion catalog sync)
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| Installs | 314 |
|---|---|
| repo stars | ★ 27.3k |
| Security audit | 2 / 3 scanners passed |
| Last updated | August 2, 2026 |
| Repository | mukul975/anthropic-cybersecurity-skills ↗ |
What it does
Detect and investigate suspicious activity in web server logs to identify potential intrusions or security breaches.
Files
Analyzing Web Server Logs for Intrusion
When to Use
- When investigating security incidents that require analyzing web server logs for intrusion
- When building detection rules or threat hunting queries for this domain
- When SOC analysts need structured procedures for this analysis type
- When validating security monitoring coverage for related attack techniques
Prerequisites
- Familiarity with security operations concepts and tools
- Access to a test or lab environment for safe execution
- Python 3.8+ with required dependencies installed
- Appropriate authorization for any testing activities
Instructions
1. Install dependencies: pip install geoip2 user-agents 2. Collect web server access logs in Combined Log Format (Apache) or Nginx default format. 3. Parse each log entry extracting: IP, timestamp, method, URI, status code, response size, user-agent, referer. 4. Apply detection rules:
- SQL injection:
UNION SELECT,OR 1=1,' OR ', hex encoding patterns - LFI/Path traversal:
../,/etc/passwd,/proc/self,php://filter - XSS:
<script>,javascript:,onerror=,onload= - Scanner signatures: nikto, sqlmap, dirbuster, gobuster, wfuzz user-agents
- Brute force: >50 POST requests to login endpoints from same IP in 5 minutes
5. Enrich with GeoIP data and generate a prioritized findings report.
python scripts/agent.py --log-file /var/log/nginx/access.log --geoip-db GeoLite2-City.mmdb --output web_intrusion_report.jsonExamples
Detect SQLi in URI
192.168.1.100 - - [15/Jan/2024:10:30:45 +0000] "GET /products?id=1' UNION SELECT username,password FROM users-- HTTP/1.1" 200 4532Scanner User-Agent Detection
Nikto/2.1.6, sqlmap/1.7, DirBuster-1.0-RC1, gobuster/3.1.0
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API Reference: Web Server Log Intrusion Analysis
Combined Log Format (Apache/Nginx)
<ip> <ident> <authuser> [<date>] "<method> <uri> <proto>" <status> <size> "<referer>" "<user-agent>"Python re Module - Log Parsing
import re
pattern = re.compile(
r'(?P<ip>\S+) \S+ \S+ \[(?P<time>[^\]]+)\] '
r'"(?P<method>\S+) (?P<uri>\S+) (?P<proto>[^"]*)" '
r'(?P<status>\d+) (?P<size>\S+) "(?P<referer>[^"]*)" "(?P<ua>[^"]*)"'
)
match = pattern.match(line)
data = match.groupdict()GeoIP2 Python Library
import geoip2.database
reader = geoip2.database.Reader("GeoLite2-City.mmdb")
response = reader.city("8.8.8.8")
response.country.name # "United States"
response.city.name # "Mountain View"
response.location.latitude # 37.386
response.location.longitude # -122.0838
reader.close()Attack Signature Categories
| Type | Example Pattern | Severity |
|---|---|---|
| SQLi | UNION SELECT, OR 1=1, SLEEP() | Critical |
| LFI | ../../etc/passwd, php://filter | High |
| XSS | <script>, onerror=, javascript: | High |
| Scanner | User-Agent: nikto, sqlmap, gobuster | Medium |
| Brute Force | >50 POST /login from same IP | High |
Scanner User-Agent Signatures
| Tool | UA Pattern |
|---|---|
| Nikto | Nikto/2.x |
| sqlmap | sqlmap/1.x |
| DirBuster | DirBuster-1.0 |
| Gobuster | gobuster/3.x |
| Wfuzz | Wfuzz/3.x |
#!/usr/bin/env python3
"""Web Server Log Intrusion Analyzer - Detects SQLi, LFI, XSS, and scanner activity in access logs."""
import re
import json
import logging
import argparse
from collections import defaultdict
from datetime import datetime
logging.basicConfig(level=logging.INFO, format="%(asctime)s [%(levelname)s] %(message)s")
logger = logging.getLogger(__name__)
COMBINED_LOG_PATTERN = re.compile(
r'(?P<ip>\S+) \S+ \S+ \[(?P<time>[^\]]+)\] '
r'"(?P<method>\S+) (?P<uri>\S+) (?P<proto>[^"]*)" '
r'(?P<status>\d+) (?P<size>\S+) "(?P<referer>[^"]*)" "(?P<ua>[^"]*)"'
)
SQLI_PATTERNS = [
(r"(?i)(union\s+(all\s+)?select)", "UNION SELECT injection"),
(r"(?i)(or\s+1\s*=\s*1)", "OR 1=1 tautology"),
(r"(?i)('\s*or\s*')", "String-based OR injection"),
(r"(?i)(;\s*drop\s+table)", "DROP TABLE injection"),
(r"(?i)(sleep\s*\(\d+\))", "Time-based blind SQLi (SLEEP)"),
(r"(?i)(benchmark\s*\(\d+)", "Time-based blind SQLi (BENCHMARK)"),
(r"(?i)(0x[0-9a-f]{8,})", "Hex-encoded payload"),
(r"(?i)(concat\s*\(|group_concat)", "Data extraction function"),
(r"(?i)(information_schema)", "Schema enumeration"),
(r"(?i)(load_file\s*\(|into\s+outfile)", "File read/write via SQL"),
]
LFI_PATTERNS = [
(r"(\.\./){2,}", "Directory traversal"),
(r"(?i)(/etc/passwd|/etc/shadow)", "Linux password file access"),
(r"(?i)(/proc/self|/proc/version)", "Proc filesystem access"),
(r"(?i)(php://filter|php://input|data://)", "PHP stream wrapper"),
(r"(?i)(c:\\windows|c:/windows)", "Windows path traversal"),
(r"(%00|%2500)", "Null byte injection"),
]
XSS_PATTERNS = [
(r"(?i)(<script[^>]*>)", "Script tag injection"),
(r"(?i)(javascript\s*:)", "JavaScript URI"),
(r"(?i)(onerror\s*=|onload\s*=|onmouseover\s*=)", "Event handler injection"),
(r"(?i)(alert\s*\(|prompt\s*\(|confirm\s*\()", "JS dialog function"),
]
SCANNER_UA_PATTERNS = [
(r"(?i)nikto", "Nikto scanner"),
(r"(?i)sqlmap", "sqlmap injection tool"),
(r"(?i)dirbuster", "DirBuster directory scanner"),
(r"(?i)gobuster", "Gobuster directory scanner"),
(r"(?i)wfuzz", "Wfuzz web fuzzer"),
(r"(?i)nmap", "Nmap scripting engine"),
(r"(?i)masscan", "Masscan port scanner"),
(r"(?i)zgrab", "ZGrab scanner"),
(r"(?i)(python-requests|python-urllib|go-http-client)", "Scripted HTTP client"),
]
def parse_log_line(line):
"""Parse a single Combined Log Format line."""
match = COMBINED_LOG_PATTERN.match(line.strip())
if not match:
return None
d = match.groupdict()
d["size"] = int(d["size"]) if d["size"] != "-" else 0
d["status"] = int(d["status"])
return d
def parse_log_file(log_path):
"""Parse all entries from a web server access log."""
entries = []
with open(log_path, "r", errors="ignore") as f:
for line in f:
entry = parse_log_line(line)
if entry:
entries.append(entry)
logger.info("Parsed %d log entries from %s", len(entries), log_path)
return entries
def detect_attacks(entries):
"""Scan log entries for attack signatures."""
findings = []
for entry in entries:
uri = entry["uri"]
ua = entry["ua"]
entry_findings = []
for pattern, desc in SQLI_PATTERNS:
if re.search(pattern, uri):
entry_findings.append({"type": "SQLi", "pattern": desc, "severity": "critical"})
for pattern, desc in LFI_PATTERNS:
if re.search(pattern, uri):
entry_findings.append({"type": "LFI", "pattern": desc, "severity": "high"})
for pattern, desc in XSS_PATTERNS:
if re.search(pattern, uri):
entry_findings.append({"type": "XSS", "pattern": desc, "severity": "high"})
for pattern, desc in SCANNER_UA_PATTERNS:
if re.search(pattern, ua):
entry_findings.append({"type": "Scanner", "pattern": desc, "severity": "medium"})
if entry_findings:
findings.append({
"ip": entry["ip"],
"timestamp": entry["time"],
"method": entry["method"],
"uri": entry["uri"][:200],
"status": entry["status"],
"user_agent": entry["ua"][:150],
"attacks": entry_findings,
})
logger.info("Detected %d suspicious requests", len(findings))
return findings
def detect_brute_force(entries, threshold=50, endpoint_patterns=None):
"""Detect brute-force login attempts by IP frequency."""
if endpoint_patterns is None:
endpoint_patterns = ["/login", "/wp-login", "/admin/login", "/api/auth", "/signin"]
ip_post_counts = defaultdict(int)
for entry in entries:
if entry["method"] == "POST":
if any(ep in entry["uri"].lower() for ep in endpoint_patterns):
ip_post_counts[entry["ip"]] += 1
brute_force = []
for ip, count in ip_post_counts.items():
if count >= threshold:
brute_force.append({"ip": ip, "post_count": count, "severity": "high"})
logger.warning("Brute force: %s sent %d POST requests to login endpoints", ip, count)
return brute_force
def enrich_with_geoip(findings, geoip_db_path):
"""Enrich findings with GeoIP location data."""
try:
import geoip2.database
reader = geoip2.database.Reader(geoip_db_path)
for finding in findings:
try:
response = reader.city(finding["ip"])
finding["geo"] = {
"country": response.country.name,
"city": response.city.name,
"latitude": response.location.latitude,
"longitude": response.location.longitude,
}
except Exception:
finding["geo"] = None
reader.close()
except ImportError:
logger.warning("geoip2 not installed, skipping GeoIP enrichment")
return findings
def summarize_attackers(findings):
"""Aggregate findings by source IP for attacker profiling."""
ip_summary = defaultdict(lambda: {"attacks": defaultdict(int), "total": 0, "uris": set()})
for f in findings:
ip = f["ip"]
ip_summary[ip]["total"] += 1
ip_summary[ip]["uris"].add(f["uri"][:100])
for attack in f["attacks"]:
ip_summary[ip]["attacks"][attack["type"]] += 1
result = []
for ip, data in sorted(ip_summary.items(), key=lambda x: x[1]["total"], reverse=True):
result.append({
"ip": ip,
"total_hits": data["total"],
"attack_types": dict(data["attacks"]),
"unique_uris": len(data["uris"]),
})
return result[:50]
def generate_report(entries, findings, brute_force, attacker_summary):
"""Generate web intrusion detection report."""
attack_counts = defaultdict(int)
for f in findings:
for a in f["attacks"]:
attack_counts[a["type"]] += 1
report = {
"timestamp": datetime.utcnow().isoformat(),
"total_log_entries": len(entries),
"suspicious_requests": len(findings),
"brute_force_sources": len(brute_force),
"attack_breakdown": dict(attack_counts),
"top_attackers": attacker_summary[:20],
"brute_force_details": brute_force,
"sample_findings": findings[:30],
}
print(f"WEB LOG ANALYSIS: {len(findings)} suspicious, {len(brute_force)} brute force sources")
return report
def main():
parser = argparse.ArgumentParser(description="Web Server Log Intrusion Analyzer")
parser.add_argument("--log-file", required=True, help="Path to access log file")
parser.add_argument("--geoip-db", help="Path to GeoLite2-City.mmdb")
parser.add_argument("--brute-threshold", type=int, default=50)
parser.add_argument("--output", default="web_intrusion_report.json")
args = parser.parse_args()
entries = parse_log_file(args.log_file)
findings = detect_attacks(entries)
brute_force = detect_brute_force(entries, args.brute_threshold)
if args.geoip_db:
findings = enrich_with_geoip(findings, args.geoip_db)
attacker_summary = summarize_attackers(findings)
report = generate_report(entries, findings, brute_force, attacker_summary)
with open(args.output, "w") as f:
json.dump(report, f, indent=2)
logger.info("Report saved to %s", args.output)
if __name__ == "__main__":
main()
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