CVE-2000-0111 is a high-severity vulnerability affecting the RightFax web client version 5.2, a product developed by avt. The vulnerability arises from the use of predictable session numbers within the web client. Session numbers (or session IDs) are intended to uniquely identify and maintain a user's session state after authentication. However, if these session identifiers are predictable, an attacker can guess or calculate valid session numbers of legitimate users. This enables remote attackers to hijack active user sessions without needing to authenticate themselves or interact with the user. The vulnerability has a CVSS score of 7.5, indicating a high risk, with an attack vector of network (AV:N), low attack complexity (AC:L), no authentication required (Au:N), and impacts on confidentiality, integrity, and availability (C:P/I:P/A:P). Since the session IDs are predictable, an attacker can perform session fixation or session hijacking attacks, gaining unauthorized access to sensitive fax communications and potentially manipulating or disrupting fax transmissions. No patch is currently available for this vulnerability, and no known exploits have been reported in the wild, but the risk remains significant due to the ease of exploitation and the critical nature of the data handled by RightFax systems.

For European organizations, the impact of this vulnerability can be substantial, especially for industries relying heavily on secure fax communications such as healthcare, legal, finance, and government sectors. Unauthorized session hijacking could lead to exposure of confidential documents, manipulation of fax transmissions, and disruption of business operations. This could result in data breaches violating GDPR regulations, leading to legal penalties and reputational damage. Additionally, attackers could use hijacked sessions to escalate privileges or move laterally within the network, increasing the scope of compromise. The availability impact could disrupt critical communication channels, affecting operational continuity. Given the lack of a patch, organizations remain exposed unless mitigations are applied.

Since no official patch is available, European organizations should implement compensating controls to mitigate the risk. These include: 1) Deploying web application firewalls (WAFs) with rules to detect and block suspicious session ID patterns or repeated session ID guessing attempts. 2) Enforcing network segmentation and strict access controls around RightFax servers to limit exposure to untrusted networks. 3) Implementing VPN or IP whitelisting to restrict access to the RightFax web client only to trusted users and networks. 4) Monitoring and logging all session activities for anomalies indicative of session hijacking attempts. 5) Encouraging users to log out after use and limiting session timeouts to reduce the window of opportunity for attackers. 6) Where possible, upgrading to newer versions or alternative fax solutions that do not exhibit this vulnerability. 7) Employing multi-factor authentication (MFA) at the network or application gateway level to add an additional layer of security despite the session ID weakness.