Summary (Bottom Line Up Front)
A Netherlands-based IP address (204.76.203.212) conducted sustained CRLF injection attacks against web infrastructure over a 29-day period from February 26 to March 27, 2026, generating 5,525 malicious events. Despite the high AbuseIPDB score (100/100), this activity is assessed as automated scanning/probing with low sophistication and minimal immediate threat to properly configured systems. Network defenders should implement standard web application security controls and monitor for similar injection attempts.
Activity Timeline
UPDATE 22026-03-31T07:25:55Z
Source: Analyst Manual Entry
A Netherlands-based IP address (204.76.203.212) conducted sustained CRLF injection attacks against web infrastructure over a 29-day period from February 26 to March 27, 2026, generating 5,525 malicious events. Despite the high AbuseIPDB score (100/100), this activity is assessed as automated scanning/probing with low sophistication and minimal immediate threat to properly configured systems. Network defenders should implement standard web application security controls and monitor for similar injection attempts.
New findings
Attack Vector: CRLF injection attempts targeting port 8080/HTTP services
Volume: 5,525 events over 29 days (average ~190 events/day)
Protocols: HTTP, TCP, TCP/SYN
Attack Patterns:
- CRLF injection (55 instances)
- CRLF injection with URL decoding (26 instances)
Source: 204.76.203.212 (Netherlands, ASN unknown)
Target Scope: Single destination port, indicating focused reconnaissance
Payload Characteristics: Standard HTTP GET requests with UTF-8 encoding manipulation and Accept-Encoding header tampering
Threat Assessment: Automated scanning tool with 95% confidence, novelty score 1/10
Recommendations
- Implement web application firewalls (WAF) with CRLF injection detection and blocking capabilities
- Configure HTTP header validation to reject malformed Accept-Encoding and other critical headers
- Monitor web server logs for unusual UTF-8 encoding patterns and header manipulation attempts
- Block traffic from 204.76.203.212 at network perimeter and consider geoblocking Netherlands-based traffic if not business-critical
- Review and harden web applications against HTTP response splitting and header injection vulnerabilities
UPDATE 12026-03-23T18:51:30Z
Source: Analyst Manual Entry
Threat actor operating from IP 204.76.203.212 (Netherlands, AS51396 Pfcloud UG) conducted sustained CRLF injection attacks against web applications over a 25-day period from February 26 to March 23, 2026. Despite 5,300 attack events and a perfect AbuseIPDB reputation score of 100/100, this activity is assessed as LOW severity reconnaissance likely preceding more sophisticated attacks. Network defenders should implement web application filtering and monitor for attack escalation.
New findings
The campaign utilized HTTP and TCP protocols targeting port 8080 exclusively, employing CRLF injection techniques (MITRE T1595.002 - Active Scanning: Vulnerability Scanning) during the reconnaissance phase of the cyber kill chain. Attack patterns included 55 instances of standard CRLF injection and 26 instances of decoded CRLF injection, both classified as medium severity. Captured payloads show UTF-8 encoded requests with manipulated Accept-Encoding headers designed to test web application input validation. The sustained 25-day attack window and high event volume (5,300 events) indicate systematic reconnaissance rather than opportunistic scanning.
Recommendations
- Block IP 204.76.203.212 and monitor AS51396 (Pfcloud UG) for additional malicious activity
- Implement web application firewall rules to detect and block CRLF injection attempts on HTTP services
- Review and harden input validation controls for web applications, particularly those accepting user-controlled headers
- Monitor port 8080 traffic for unusual HTTP request patterns and header manipulation attempts
- Establish enhanced logging for reconnaissance activities that may indicate preparation for follow-on attacks
INITIAL REPORT2026-03-14T17:33:23Z
Source: batch_hunting
IP address 204.76.203.212 (Netherlands) conducted sustained CRLF injection attacks against web infrastructure over a 16-day period from February 26 to March 14, 2026, generating over 4,000 malicious events. The threat actor demonstrates persistent reconnaissance behavior with a perfect AbuseIPDB reputation score, indicating established malicious infrastructure. Immediate blocking and enhanced web application monitoring are recommended.
Technical details
The threat actor leveraged HTTP and TCP protocols to deliver CRLF injection payloads, generating 4,039 events targeting a single destination port. Attack patterns included both standard and decoded CRLF injection techniques (81 total hits), suggesting automated tooling with evasion capabilities. The campaign aligns with MITRE ATT&CK reconnaissance phase activities, though specific technique mapping requires additional analysis. Key IOC: 204.76.203.212 (ASN unknown, no reverse DNS resolution).
IOCs
IP:204.76.203.212
COUNTRY:NL
Recommendations
- Block IP address 204.76.203.212 at network perimeter and web application firewalls immediately
- Implement enhanced logging and monitoring for CRLF injection attempts across all web-facing applications
- Review and strengthen input validation controls, particularly for HTTP header manipulation attacks
- Conduct threat hunting for similar attack patterns targeting port 8080 and other web services
- Monitor for follow-on activity from the Netherlands IP space and correlate with existing threat intelligence feeds