What are the most common false positives generated by an IDS?

2 Network anomalies

Another cause of false positives is network anomalies, which are deviations from the normal or expected behavior of the network. These can include changes in traffic volume, patterns, sources, or destinations, as well as errors, failures, or misbehaviors of network components. For example, if the IDS detects a sudden spike in traffic from an unusual source, it can alert for a possible denial-of-service attack, when in fact it could be a legitimate backup process, a network scan, or a misconfigured router. To reduce this, you should monitor and baseline your network activity, and use anomaly-based IDS that can learn and adapt to the network behavior.

3 False alarms

A third cause of false positives is false alarms, which are alerts that are triggered by harmless or authorized activities that resemble attacks. These can include testing, debugging, auditing, or maintenance tasks that involve scanning, probing, or injecting data into the network. For example, if the IDS detects a port scan from an internal IP address, it can alert for a possible reconnaissance attack, when in fact it could be a security assessment, a troubleshooting procedure, or a network discovery tool. To prevent this, you should coordinate and communicate your network activities with your security team, and whitelist or exclude known and trusted sources from the IDS.

4 Ambiguous traffic

A fourth cause of false positives is ambiguous traffic, which is traffic that has multiple or unclear meanings or interpretations. This can include encrypted, compressed, fragmented, or obfuscated traffic that the IDS cannot fully analyze or understand. For example, if the IDS detects a packet that contains a suspicious string or pattern, it can alert for a possible exploit, when in fact it could be a legitimate application, a harmless file, or a random coincidence. To avoid this, you should decrypt, decompress, reassemble, or deobfuscate your traffic before sending it to the IDS, or use IDS that can handle these types of traffic.

5 Evolving threats

A fifth cause of false positives is evolving threats, which are new or emerging attacks that the IDS does not recognize or anticipate. These can include zero-day exploits, advanced persistent threats, polymorphic malware, or stealthy techniques that bypass or evade the IDS. For example, if the IDS detects a normal-looking packet that contains a hidden or embedded payload, it can miss or ignore a possible attack, and later alert for a false positive when the payload is executed or activated. To reduce this, you should update and supplement your IDS with additional sources of intelligence, such as threat feeds, honeypots, or behavioral analysis.

False positives are inevitable in any IDS, but they can be minimized and managed with proper configuration, monitoring, coordination, and intelligence. By understanding the most common causes and types of false positives, you can improve your network security and efficiency.