CVE-2025-10533 is an integer overflow vulnerability identified in the Scalable Vector Graphics (SVG) component of Mozilla Firefox and Thunderbird. This vulnerability affects Firefox versions earlier than 143, Firefox ESR versions earlier than 115.28 and 140.3, and Thunderbird versions earlier than 143 and 140.3. The root cause is an integer overflow (CWE-190) that occurs when processing SVG content, which can lead to memory corruption. Exploiting this flaw allows remote attackers to execute arbitrary code with high impact on confidentiality, integrity, and availability. The CVSS 3.1 base score is 8.8, indicating a high severity level, with an attack vector of network (AV:N), low attack complexity (AC:L), requiring privileges (PR:L), no user interaction (UI:N), and unchanged scope (S:U). The vulnerability does not require user interaction, making it easier to exploit remotely by sending crafted SVG content to vulnerable clients. Although no known exploits are currently reported in the wild, the potential for exploitation is significant given the widespread use of Firefox and Thunderbird. The vulnerability was publicly disclosed on September 16, 2025, and no official patches or mitigation links were provided at the time of disclosure, emphasizing the need for vigilance and rapid response once patches become available.

For European organizations, this vulnerability poses a substantial risk due to the widespread use of Firefox and Thunderbird in both enterprise and public sectors. Successful exploitation could lead to remote code execution, allowing attackers to gain unauthorized access, steal sensitive data, disrupt services, or deploy malware. The impact spans confidentiality breaches, integrity violations through code manipulation, and availability disruptions via potential denial-of-service conditions. Sectors such as government, finance, healthcare, and critical infrastructure, which rely heavily on secure web browsing and email communication, are particularly vulnerable. The lack of user interaction requirement increases the threat level, as attackers can exploit the vulnerability through malicious web content or email attachments without user awareness. This could facilitate targeted attacks, espionage, or widespread malware campaigns affecting European digital ecosystems.

European organizations should implement the following specific mitigation strategies: 1) Monitor Mozilla’s official channels closely for the release of security patches addressing CVE-2025-10533 and prioritize immediate deployment of these updates across all affected Firefox and Thunderbird installations. 2) Employ network-level protections such as web filtering and email scanning to block or quarantine SVG content from untrusted sources, reducing exposure to crafted malicious payloads. 3) Restrict the use of outdated Firefox and Thunderbird versions by enforcing software inventory and compliance policies, ensuring no vulnerable versions remain in operational environments. 4) Utilize endpoint detection and response (EDR) tools to identify anomalous behaviors indicative of exploitation attempts, such as unexpected process executions or memory corruption signs. 5) Educate users about the risks of opening unsolicited web content or email attachments, even though user interaction is not required for exploitation, to reinforce overall security posture. 6) Consider deploying application sandboxing or isolation techniques for browsers and email clients to limit the impact of potential exploits. 7) Coordinate with incident response teams to prepare for rapid containment and remediation in case exploitation attempts are detected.