Non-Standard Port T1571
Tactic: Command & Control
Adversaries may communicate using a protocol and port pairing that are typically not associated. For example, HTTPS over port 8088 or port 587 as opposed to the traditional port 443. Adversaries may make changes to the standard port used by a protocol to bypass filtering or muddle analysis/parsing of network data.
Events covered
11 catalog events are tagged with this technique by at least one rule.
Authoring guide
Patterns shared across the 27 rules above: which fields they filter on, what specific values they look for, and what they exclude. The catalog normalizes field names across vendors so Sigma's Image, Elastic's process.name, and Splunk's process_name collapse into one row. Each rule contributes at most once per row.
Fields filtered most (58 distinct)
The fields most rules look at when detecting this technique. The How column shows the operators authors use (eq, wildcard, regex_match, match) and how often each appears. Sample values are concrete examples to start from, not an exhaustive list.
Top indicator values (251 distinct)
Specific (field, operator, value) combinations the rules check for, ranked by how many rules under this technique use each one. The Corpus reach column counts how many rules across the entire catalog (any technique) check the same combination. High numbers point to widely-used indicators that are likely noisy on their own; combine them with another condition for useful signal. Blank means the combination is specific to rules under this technique. Click a value to expand the rules under this technique that use it.
Exclusions (116 distinct)
Field/operator/value combinations excluded by rules under this technique (top-level not() clauses), sorted by how many rules exclude each. These are the false-positive paths the community has learned to filter out. A new rule that ignores the high-count entries here will likely fire on the same noisy paths. Click a value to expand the rules under this technique that exclude it.
Rules under this technique
Every rule in the catalog tagged with this technique, grouped by vendor. Click a rule title for its full predicates, exclusions, and indicators.
Sigma 5 rules
- Communication To Uncommon Destination Ports
- Potentially Suspicious Malware Callback Communication
- Potentially Suspicious Malware Callback Communication - Linux
- Suspicious DNS Z Flag Bit Set
- Testing Usage of Uncommonly Used Port
Elastic 7 rules
- Deprecated - Uncommon Destination Port Connection by Web Server
- Potential Data Exfiltration Activity to an Unusual Destination Port
- Script Interpreter Connection to Non-Standard Port
- SMTP on Port 26/TCP
- Suricata and Elastic Defend Network Correlation
- Suspicious Outbound Network Connection via Unsigned Binary
- Unusual Linux Network Port Activity
Splunk 4 rules
- Cisco NVM - Outbound Connection to Suspicious Port
- Cisco Secure Firewall - Communication Over Suspicious Ports
- Cisco Secure Firewall - File Download Over Uncommon Port
- Ollama Abnormal Network Connectivity
Kusto 9 rules
- Abnormal Port to Protocol
- Fortinet - Beacon pattern detected
- GSA - Detect Abnormal Deny Rate for Source to Destination IP
- GSA - Detect Protocol Changes for Destination Ports
- Palo Alto - potential beaconing detected
- Palo Alto - potential beaconing detected
- Potential beaconing activity (ASIM Network Session schema)
- Ubiquiti - Connection to known malicious IP or C2
- Ubiquiti - Possible connection to cryptominning pool