In Suricata, a popular open-source network threat detection engine, rules are typically written to match specific patterns in network traffic. While Suricata does support regular expressions (regex) for complex pattern matching, you asked about matching a literal string repeated twice or more without using regex.
Suricata's rule language includes various keywords and options for pattern matching, but it doesn't natively support the concept of repeating strings directly without using regex. However, you can achieve similar functionality by writing multiple content matches within the same rule.
Here's an example of how you might write a Suricata rule to match a literal string "example" that appears at least twice in the payload:
alert tcp any any -> any any (msg:"Example string repeated"; content:"example"; content:"example"; sid:1000001;)
In this rule:
alertspecifies the action to take when the rule matches.tcpspecifies the protocol.any any -> any anyspecifies that the rule applies to traffic from any source IP/port to any destination IP/port.msg:"Example string repeated"is a message that will be logged when this rule matches.content:"example"is used twice to specify that "example" must appear at least twice in the payload.sid:1000001is a unique identifier for this rule.
This approach works because each content keyword looks for its specified pattern independently. By including multiple content keywords with the same value, you're effectively requiring that value to appear multiple times in order for the rule to match.
However, note that this method has limitations:
- It requires exact positioning if there are constraints on where these strings should appear relative to each other.
- It may not be as efficient as using regex for more complex patterns or larger datasets.
For more advanced scenarios where precise control over repetitions and positions is needed, using regex would be more appropriate despite your preference against it.