CVE-1999-1289 in ICQ
Summary
by MITRE
ICQ 98 beta on Windows NT leaks the internal IP address of a client in the TCP data segment of an ICQ packet instead of the public address (e.g. through NAT), which provides remote attackers with potentially sensitive information about the client or the internal network configuration.
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Analysis
by VulDB Data Team • 04/17/2026
The vulnerability described in CVE-1999-1289 represents a significant information disclosure issue within the ICQ 98 beta client implementation on Windows NT systems. This flaw manifests as an improper handling of network address information during the transmission of ICQ packets, specifically affecting how the client manages TCP data segments that contain internal IP addresses rather than the appropriate public addresses. The issue occurs when the ICQ client operates within a network environment that utilizes Network Address Translation, where internal private IP addresses should be masked by the public-facing NAT address. However, the vulnerable client implementation fails to properly translate these addresses, resulting in the exposure of internal network topology information.
The technical nature of this vulnerability stems from the client's failure to properly implement address translation mechanisms within its network communication stack. When ICQ packets are transmitted over the internet, the TCP data segments contain source IP addresses that should reflect the public address of the NAT device rather than the internal private IP address of the client machine. This improper address handling creates a direct information leak that exposes internal network configuration details to remote attackers. The vulnerability specifically impacts Windows NT systems running the ICQ 98 beta client, where the network stack implementation does not adequately manage the distinction between internal and external addressing.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with critical network topology information that can be leveraged in subsequent attack phases. By obtaining the internal IP address, remote adversaries gain insight into the internal network structure, potentially identifying network segments, firewall configurations, and internal host mappings. This information can significantly aid in network reconnaissance activities and may enable more sophisticated attacks such as internal network scanning or targeted exploitation of internal services. The vulnerability essentially undermines the security benefits provided by NAT, creating a direct pathway for attackers to bypass network boundary protections that are typically effective against external threats.
This vulnerability aligns with CWE-200, which addresses "Information Exposure," and demonstrates how improper address handling can lead to sensitive information disclosure. The issue also relates to ATT&CK technique T1046, "Network Service Scanning,' as the leaked information can be used to identify internal network services and hosts. Additionally, the vulnerability connects to T1082, "System Information Discovery," as it provides attackers with detailed information about the internal network configuration. The flaw represents a classic case of inadequate network address translation implementation, where the client fails to properly abstract the internal network topology from external observers. Organizations affected by this vulnerability should implement immediate mitigations including network segmentation, firewall rules to restrict ICQ traffic, and potentially updating to patched versions of the ICQ client that properly handle address translation.
The long-term implications of this vulnerability highlight the importance of proper network address handling in client applications, particularly those operating in NAT environments. It demonstrates how seemingly minor implementation flaws in network communication protocols can create significant security risks by exposing internal network information. The vulnerability serves as a reminder of the critical need for thorough security testing of network applications, especially those that operate in complex network environments with multiple address translation layers. Organizations should ensure that all network applications properly handle address translation and do not inadvertently expose internal network information through their communication protocols.