CVE-2001-0411 in Reliant Unix
Summary
by MITRE
Reliant Unix 5.44 and earlier allows remote attackers to cause a denial of service via an ICMP port unreachable packet, which causes Reliant to drop all connections to the source address of the packet.
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Analysis
by VulDB Data Team • 04/08/2019
The vulnerability described in CVE-2001-0411 represents a significant denial of service weakness in Reliant Unix operating systems version 5.44 and earlier. This flaw manifests when the system receives an ICMP port unreachable packet, triggering a cascading failure that results in the complete disruption of all network connections originating from the source address of the malicious packet. The vulnerability exploits the operating system's inadequate handling of ICMP error messages, specifically those indicating port unreachability, which are typically used by network protocols to communicate that a destination port is unavailable or unreachable.
The technical implementation of this vulnerability stems from the improper processing of ICMP port unreachable messages within the network stack of Reliant Unix. When such a packet is received, the system's network protocol handler fails to properly validate or sanitize the incoming ICMP message before executing its processing logic. This inadequate input validation creates an exploitable condition where an attacker can craft and send a specifically formatted ICMP port unreachable packet that triggers the system's connection dropping mechanism. The flaw essentially causes the system to indiscriminately terminate all active connections from the source address that sent the malicious packet, effectively creating a denial of service condition that impacts legitimate network traffic and service availability.
From an operational impact perspective, this vulnerability presents a severe threat to network availability and system reliability in environments running Reliant Unix 5.44 or earlier versions. The attack requires minimal resources from the attacker, who only needs to send a single ICMP port unreachable packet to potentially disrupt all connections from a targeted source address. This makes the vulnerability particularly dangerous in production environments where service availability is critical, as it can be exploited by both malicious actors and automated attack tools. The cascading effect of connection drops can lead to widespread service disruption, potentially affecting multiple applications and services that depend on the affected system's network connectivity, making this a high-impact vulnerability from a business continuity standpoint.
The vulnerability aligns with CWE-20, which describes improper input validation, and represents a classic example of how network protocol implementations can be exploited to create denial of service conditions. From an adversarial perspective, this flaw fits within the ATT&CK framework under the T1498 technique for Network Denial of Service, where adversaries leverage system weaknesses to disrupt network services. The exploitability of this vulnerability is enhanced by the fact that ICMP port unreachable messages are commonly used and expected network traffic, making it difficult to distinguish between legitimate and malicious packets. Organizations should implement immediate mitigations including applying vendor patches, configuring network firewalls to filter suspicious ICMP traffic, and implementing connection tracking mechanisms that can detect and prevent such exploitation patterns. Additionally, system administrators should consider network segmentation and monitoring solutions to detect unusual connection dropping patterns that may indicate exploitation attempts.