CVE-2025-49710 is a critical integer overflow vulnerability identified in the OrderedHashTable component of the JavaScript engine used by Mozilla Firefox versions prior to 139.0.4. The OrderedHashTable is a data structure that manages key-value pairs while preserving insertion order, and it is integral to JavaScript execution within the browser. An integer overflow occurs when an arithmetic operation attempts to create a numeric value that exceeds the maximum size the integer type can hold, causing the value to wrap around unexpectedly. In this context, the overflow can lead to memory corruption, potentially allowing an attacker to execute arbitrary code, escalate privileges, or cause a denial of service. The vulnerability is remotely exploitable without requiring any user interaction or privileges, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N). This means an attacker can craft malicious web content or scripts that trigger the overflow when processed by the vulnerable Firefox JavaScript engine. The CVSS score of 9.8 (critical) reflects the high impact on confidentiality, integrity, and availability, with an easy attack vector and no prerequisites. Although no exploits are currently known in the wild, the severity and ease of exploitation make this a significant threat. The lack of patch links suggests that a fix is either pending or not yet publicly available, increasing the urgency for users and organizations to update promptly once a patch is released.

For European organizations, this vulnerability poses a serious risk due to the widespread use of Mozilla Firefox as a primary web browser in both enterprise and public sectors. Successful exploitation could lead to unauthorized access to sensitive data, disruption of critical services, and potential lateral movement within corporate networks. Given the browser's role as a gateway to internet resources, attackers could leverage this flaw to deploy malware, steal credentials, or compromise internal systems. The vulnerability's ability to affect confidentiality, integrity, and availability simultaneously means that organizations could face data breaches, operational downtime, and reputational damage. Sectors such as finance, healthcare, government, and critical infrastructure in Europe, which rely heavily on secure web browsing, are particularly vulnerable. Additionally, the remote and unauthenticated nature of the exploit increases the likelihood of widespread attacks, especially targeting users who delay updating their browsers.

European organizations should take immediate steps to mitigate this threat beyond generic advice. First, enforce rapid deployment of Firefox updates, specifically upgrading to version 139.0.4 or later once available. Until patches are released, consider implementing network-level protections such as web filtering to block access to untrusted or suspicious websites that could host exploit code. Employ browser isolation technologies that execute web content in sandboxed environments to contain potential exploits. Conduct targeted user awareness campaigns emphasizing the risks of visiting untrusted sites and the importance of timely browser updates. Additionally, monitor network traffic and endpoint behavior for anomalies indicative of exploitation attempts, such as unexpected JavaScript execution patterns or memory corruption indicators. Organizations should also review and tighten browser security configurations, disabling unnecessary JavaScript features or extensions that could increase attack surface. Finally, maintain an incident response plan ready to address potential exploitation scenarios promptly.