How do attackers use ICMP Information Request?

What ICMP Information Request is actually used for in an attack path

icmp information request is a legacy query type, so attackers treat it as a low-noise probe rather than a primary intrusion method. A response tells them something about reachability, protocol handling, or weak filtering. The value is in confirmation: it can help distinguish a live host from dead space and reveal where perimeter controls are inconsistent.

That is why this technique usually appears in reconnaissance, not exploitation. It is most useful when the defender has left older ICMP handling in place or when a network path allows unnecessary diagnostic traffic through. In practice, it is one small signal inside a broader exposure-mapping workflow, not a standalone break-in vector.

What a response tells an attacker about your network

When a host answers the request, the attacker gains a cheap validation point. The response can indicate that the target is reachable, that a filter is permitting rare ICMP types, or that internal segmentation is weaker than expected. If several hosts answer, the pattern can also hint at address ranges worth scanning more aggressively.

The result is especially useful because modern defenders often ignore this ICMP type. That makes any reply more interesting than a routine ping in some environments. Attackers can combine it with other passive or active probes to build a map of which systems are exposed, which ones are filtered, and where policy exceptions may exist.

Because this is a legacy protocol feature, the safest interpretation is simple: any unexpected answer should be treated as an exposure signal until proven otherwise. The point is not that the request alone is dangerous, but that it can validate the presence of systems the operator may have assumed were invisible.

How defenders should think about suppression, logging, and verification

From a defensive perspective, the question is not whether every ICMP message should be blocked. It is whether this specific type is necessary anywhere on the network and, if not, whether it is being suppressed consistently at the perimeter and inside trust boundaries. If it is allowed for a narrow operational reason, it should be explicitly documented and monitored.

Operationally, the right response is to treat legacy network protocols as exposure points and verify that your filtering policy matches current use, not historical habit. Repeated probes from the same source should be correlated with firewall, IDS, and edge telemetry so that reconnaissance does not blend into background noise.

Defenders should also validate whether any hosts that answer are supposed to be reachable at all. If the answer is yes, the exposure is probably intentional; if not, the response may indicate misconfiguration, overbroad routing, or a missing control on an older system. That distinction matters more than the ICMP packet itself.

Risk and Threat Considerations

ICMP Information Request is a reconnaissance primitive, so the main risk is information leakage about live systems and control coverage. Even a small response can reduce uncertainty for an attacker and help them prioritise later scans, especially when the network is expected to hide or restrict legacy diagnostic traffic.

Failure mechanism: The request succeeds because a host, firewall rule, or intermediate device still permits a legacy ICMP type that is no longer needed for normal operations. That creates a low-cost oracle for reachability and can expose segmentation gaps or inconsistent perimeter enforcement.

Impact: Attackers can use the signal to focus scanning, identify reachable assets, and refine their attack surface map before moving to more effective probes. In a poorly governed environment, repeated responses can also reveal which systems are insufficiently hardened or which exceptions have accumulated over time.

Practitioner Guidance

What to verify: Confirm whether any business or operational function truly requires ICMP Information Request to be accepted. If not, block it consistently at egress and ingress points, and make sure the decision is reflected in both host and network controls.

What to measure: Track repeated ICMP probes from the same source, especially when they target multiple subnets or occur alongside broader scan activity. A single isolated packet may be noise, but a pattern of legacy ICMP requests is usually reconnaissance.

Common mistake: Treating “rarely used” as “harmless.” Rare protocols are often valuable to attackers precisely because defenders overlook them, so the control objective is to remove unnecessary response paths, not to rely on obscurity.

Practitioner takeaway: If a legacy ICMP type does not serve an explicit operational need, the safest posture is to suppress it and treat any replies as a signal that exposure review is overdue.

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