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OSSEC / HIDS Rule 4151

Rule family: OSSEC / HIDS
Rule ID: 4151
Definition status: Present in current source
Alert message / subject: Firewall: Multiple drop events from same source.
Rule level: 7
Definition checked: 2026-10-21
Configured frequency: 8
Timeframe (seconds): 120
Ignore interval (seconds): 240

Correlation values are configuration attributes; event-count behavior depends on the manager version and parent rules.

Interpretation and response

This event is recorded as “Firewall: Multiple drop events from same source.” Review the originating log and the affected host or service to determine whether the activity was expected.

An OSSEC/HIDS event records or correlates activity. Blocking depends on the originating application and any separately configured Active Response policy; an alert alone does not prove that an attack was blocked.

Documentation

The following guidance was migrated from the historical wiki and reviewed against the rule definition. Legacy ASL product names and interface instructions refer to the versions documented then. Use the current metadata above and your installed configuration when interpreting thresholds, notification settings and response behavior.

Description

ASL has detected multiple attempts to access a port that you have configured the ASL firewall to block, and ASL has blocked this access. ASL does not block any ports by default. It will only block the ports you configure it to block. Therefore, if you are getting these alerts, this means you have configured ASL to block this port. See the Tuning guidance section below for instructions to configure ASLs firewall to allow connections to ports you have configured.

When ASL detects this has occurred multiple times, it will also shun the IP address based on the OSSEC_SHUN_TIME (historical reference) you have configured for your system.

The Linux kernel also supports stateful packet inspection. This rule can also be triggered if a connection is broken and is repeatedly generating out of sequence packetsThis is not a bug in ASL (historical reference) or in the kernel. This is exactly what stateful packet inspection is supposed to do. If you are triggering this rule on allowed traffic, please make sure you have FW_DROP_INVALID (historical reference) enabled for your system. This will detect these non-malicious out of sequence packets, and will ignore them.

Note: Some third party kernels do not support stateful packet inspection. The ASL kernel supports stateful packet inspection. If your kernel does not, or does not include the INVALID state for iptables then you will need to disable active response on this rule. Some third party kernels provided with openvz and virtuzzo are known to have this limitation.

How to read the firewall logs

The ASL firewall will log a lot of information about a connection it has blocked because you have configured ASL to block the port. See this page for documentation about the log format for ASL:

Firewall Logs (historical reference)

Troubleshooting

False Positives

None.

If you do not wish to block access to this port, please see the Tuning Guidance below.

Tuning Guidance

To configure the firewall to allow connections to this port, please see the ASL firewall documentation page.

If you are using Fast mode, then you will want to add the ports you want to allow in to these settings:

ASL firewall (historical reference)

Additional Information

FAQs

See this Article:

Using ASL (historical reference)

Source and revision

Migrated from HIDS_4151, wiki page 424, revision 5391 (20150226). Documentation review: 2026-10-21. An archived wiki status of Active is not a current deployment status.

For assistance, provide the rule ID, installed product and rule version, and a sanitized event to Atomicorp support .