CVE-2025-53603 is a high-severity vulnerability identified in Alinto SOPE's SOGo versions 2.0.2 through 5.12.2. The root cause is a NULL pointer dereference in the sope-core component, specifically within the NGExtensions/NGHashMap.m source file. This occurs when a crafted request contains a query string parameter that duplicates a parameter present in the POST body. The software fails to properly handle this condition, leading to a NULL pointer dereference and subsequent crash of the SOGo service. This vulnerability falls under CWE-476, which relates to NULL pointer dereference errors that can cause application crashes or denial of service. The CVSS v3.1 base score is 7.5, indicating a high severity, with the vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. This means the vulnerability is remotely exploitable over the network without authentication or user interaction, and it impacts availability only, causing service disruption but not compromising confidentiality or integrity. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability affects a widely used open-source groupware server, SOGo, which is deployed in various enterprise and institutional environments for email, calendaring, and collaboration services. The crash caused by this NULL pointer dereference can lead to denial of service, interrupting critical communication and collaboration functions.

For European organizations relying on Alinto SOPE's SOGo for email and groupware services, this vulnerability poses a significant risk of service disruption. The denial of service caused by the crash can interrupt business communications, delay workflows, and reduce productivity. Organizations in sectors such as government, education, healthcare, and finance that depend on continuous availability of collaboration tools may experience operational impacts. Additionally, repeated exploitation attempts could lead to persistent outages, requiring emergency response and recovery efforts. Although the vulnerability does not directly expose sensitive data or allow unauthorized access, the loss of availability can indirectly affect confidentiality and integrity by forcing fallback to less secure communication channels or causing delays in security incident responses. The fact that no authentication or user interaction is required for exploitation increases the threat level, as attackers can remotely trigger crashes without insider access or user involvement.

To mitigate this vulnerability, European organizations should prioritize the following actions: 1) Monitor official Alinto and SOGo project channels for the release of security patches addressing CVE-2025-53603 and apply them promptly. 2) In the absence of an immediate patch, implement network-level protections such as web application firewalls (WAFs) to detect and block requests containing duplicate parameters in query strings and POST bodies. Custom rules can be developed to identify this anomaly. 3) Employ rate limiting and anomaly detection on the SOGo service endpoints to reduce the risk of denial of service through repeated exploitation attempts. 4) Conduct internal testing in a controlled environment to reproduce the issue and validate any temporary workarounds or mitigations. 5) Ensure robust monitoring and alerting on SOGo service availability to detect crashes quickly and enable rapid incident response. 6) Consider deploying redundant or failover groupware infrastructure to maintain service continuity during potential outages. 7) Educate IT and security teams about this vulnerability to increase awareness and readiness to respond.