CVE-1999-1172 is a vulnerability found in Maximizer Enterprise version 4, specifically in its calendar and address book program. The issue arises from the design of the software's shared calendar functionality, which allows any arbitrary user to modify the calendar entries of other users without proper access controls or authentication. This means that when calendars are shared among users, there is no restriction preventing unauthorized users from altering calendar data belonging to others. The vulnerability does not affect confidentiality or availability directly but impacts the integrity of calendar information. The CVSS score is 5.0 (medium severity), with the vector AV:N/AC:L/Au:N/C:N/I:P/A:N, indicating that the vulnerability can be exploited remotely over the network without authentication, requires low attack complexity, and results in partial integrity compromise without affecting confidentiality or availability. There is no patch available for this vulnerability, and no known exploits have been reported in the wild. Given the age of the software (version 4, published in 1999), this vulnerability is primarily relevant in legacy environments still using this product. The vulnerability could be exploited by an attacker or unauthorized user with network access to the Maximizer Enterprise calendar system to alter calendar entries, potentially causing confusion, misinformation, or disruption of scheduling and communication within an organization.

For European organizations still using Maximizer Enterprise version 4, this vulnerability could lead to unauthorized modification of shared calendar data, undermining trust in scheduling and communication tools. While it does not directly expose sensitive data or cause system downtime, the integrity compromise could disrupt business operations, meetings, and coordination efforts. In sectors where precise scheduling is critical—such as healthcare, finance, or government—such disruptions could have cascading effects on service delivery or decision-making. Additionally, malicious actors could exploit this to insert misleading information, potentially facilitating social engineering or insider threat activities. However, given the age and likely limited deployment of this software today, the overall impact is expected to be limited to legacy systems without modern security controls.

Since no patch is available for this vulnerability, organizations should consider the following specific mitigations: 1) Disable calendar sharing features in Maximizer Enterprise 4 if possible, to prevent unauthorized modifications. 2) Restrict network access to the Maximizer Enterprise server to trusted users and segments only, using network segmentation and firewall rules to limit exposure. 3) Implement strict user access controls and monitor user activities on the calendar system to detect unauthorized changes. 4) Where feasible, migrate from Maximizer Enterprise 4 to a modern, supported calendaring solution that enforces proper access controls and authentication. 5) Educate users about the risks of shared calendar modifications and encourage verification of critical scheduling information through secondary channels. 6) Regularly audit calendar data integrity and maintain backups to restore correct information if unauthorized changes occur.