CVE-2025-9817 is a high-severity vulnerability identified in the Wireshark network protocol analyzer, specifically affecting versions 4.4.0 through 4.4.8. The vulnerability is classified under CWE-476, which corresponds to a NULL Pointer Dereference. This flaw occurs within the SSH dissector component of Wireshark, which is responsible for parsing and analyzing SSH protocol traffic. When processing crafted SSH packets, the dissector may dereference a NULL pointer, leading to a crash of the Wireshark application. This results in a denial of service (DoS) condition, where the affected application becomes unavailable or unresponsive. The CVSS v3.1 base score is 7.8, indicating a high severity level. The vector string CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H reveals that the attack requires local access (AV:L), low attack complexity (AC:L), no privileges (PR:N), and user interaction (UI:R). The impact affects confidentiality, integrity, and availability (all rated high), meaning that exploitation could lead to significant disruption and potential exposure or manipulation of sensitive data. Although no known exploits are currently reported in the wild, the vulnerability's presence in a widely used tool like Wireshark makes it a critical issue to address promptly. Wireshark is extensively used by network administrators, security analysts, and forensic investigators to capture and analyze network traffic, making this vulnerability particularly impactful in environments where SSH traffic analysis is routine.

For European organizations, the impact of CVE-2025-9817 can be significant due to the widespread use of Wireshark in IT, cybersecurity, and network operations teams. A successful exploitation could disrupt network monitoring and incident response activities by causing Wireshark to crash, potentially delaying the detection and analysis of malicious network activity. This denial of service could also lead to temporary loss of visibility into SSH traffic, which is critical for secure remote access and management. Confidentiality and integrity impacts are also high, as the vulnerability could be leveraged to interfere with the analysis of sensitive SSH communications, possibly masking malicious activity or data exfiltration attempts. Organizations in sectors such as finance, telecommunications, government, and critical infrastructure—where SSH is heavily used for secure communications—may face increased risk. Additionally, the requirement for local access and user interaction implies that insider threats or targeted attacks against analysts using Wireshark could exploit this vulnerability. The disruption could affect compliance with European data protection regulations (e.g., GDPR) if incident response capabilities are impaired.

To mitigate CVE-2025-9817, European organizations should take the following specific actions: 1) Immediately upgrade Wireshark to the latest patched version once available, as no patches are currently linked but are expected to be released promptly given the vulnerability's severity. 2) Until patches are applied, restrict Wireshark usage to trusted personnel and environments to minimize exposure to crafted malicious SSH traffic. 3) Implement strict access controls on systems running Wireshark to prevent unauthorized local access, including enforcing least privilege principles and multi-factor authentication. 4) Educate users about the risk of opening untrusted capture files or analyzing suspicious SSH traffic that could trigger the vulnerability. 5) Employ network segmentation to isolate monitoring tools from untrusted network segments where malicious traffic might originate. 6) Monitor logs and system behavior for signs of Wireshark crashes or abnormal terminations that could indicate exploitation attempts. 7) Consider alternative or additional network analysis tools that do not exhibit this vulnerability during the interim period. These targeted steps go beyond generic advice by focusing on controlling local access, user interaction risks, and operational practices specific to Wireshark and SSH traffic analysis.