CVE-2025-1991 is a high-severity vulnerability affecting IBM Informix Dynamic Server versions 12.10, 14.10, and 15.0. The root cause is an integer underflow (CWE-191) occurring during packet processing. Integer underflow happens when an arithmetic operation causes a value to wrap around below its minimum representable value, potentially leading to unexpected behavior. In this case, the underflow can be triggered remotely without authentication or user interaction, allowing an attacker to send specially crafted packets to the server. This can cause the server to crash or become unresponsive, resulting in a denial of service (DoS). The vulnerability has a CVSS v3.1 base score of 7.5, reflecting its high impact on availability with no impact on confidentiality or integrity. The attack vector is network-based (AV:N), requires no privileges (PR:N), and no user interaction (UI:N), making it relatively easy to exploit. No known exploits are currently reported in the wild, and no patches or mitigations have been explicitly linked in the provided data. IBM Informix Dynamic Server is a relational database management system used in enterprise environments for critical data storage and processing. A DoS condition in such a system can disrupt business operations, data availability, and service continuity.

For European organizations relying on IBM Informix Dynamic Server in versions 12.10, 14.10, or 15.0, this vulnerability poses a significant risk to service availability. A successful attack could cause database outages, impacting applications and services dependent on the database backend. This can lead to operational downtime, loss of productivity, and potential financial losses. Industries such as finance, manufacturing, telecommunications, and public sector entities that use Informix for transaction processing or data warehousing could be particularly affected. Additionally, prolonged downtime could affect compliance with data availability regulations under GDPR if critical services are disrupted. Although the vulnerability does not allow data breach or modification, the denial of service could indirectly affect business continuity and customer trust.

Organizations should immediately assess their use of IBM Informix Dynamic Server versions 12.10, 14.10, and 15.0. Since no patch links are provided, it is critical to monitor IBM’s official security advisories for updates or patches addressing CVE-2025-1991. In the interim, network-level mitigations should be implemented: restrict access to Informix server ports to trusted hosts only via firewall rules; deploy intrusion detection/prevention systems (IDS/IPS) to detect and block anomalous or malformed packets targeting Informix; apply rate limiting to reduce the risk of DoS attacks; and ensure robust network segmentation to isolate database servers from untrusted networks. Additionally, review and harden Informix server configurations to minimize exposure. Regular backups and tested recovery procedures should be in place to restore service quickly if a DoS occurs. Finally, conduct security awareness and incident response drills focusing on database availability threats.