CVE-2025-6424 is a use-after-free vulnerability identified in the FontFaceSet component of Mozilla Firefox. This vulnerability affects Firefox versions prior to 140, Firefox ESR versions prior to 115.25, and Firefox ESR versions prior to 128.12. The use-after-free flaw occurs when the FontFaceSet object, which manages font faces in the browser, is improperly handled in memory, leading to a situation where the program continues to use memory after it has been freed. This can result in a crash and potentially allow an attacker to execute arbitrary code or escalate privileges within the context of the browser process. The vulnerability is exploitable through crafted web content that triggers the faulty font handling logic. Although no public exploits have been reported in the wild as of the publication date, the nature of use-after-free vulnerabilities in browser components is typically high-risk due to the browser’s exposure to untrusted web content. The lack of a CVSS score indicates that the vulnerability is newly disclosed and has not yet been fully assessed or scored by standard frameworks. The vulnerability’s impact is primarily on the confidentiality, integrity, and availability of the user’s system through potential remote code execution or denial of service via browser crash. Since Firefox is widely used across many platforms, this vulnerability has broad implications for users who have not updated to the patched versions. The absence of patch links suggests that fixes may be pending or recently released but not yet widely documented.

For European organizations, this vulnerability poses a significant risk due to the widespread use of Mozilla Firefox in both enterprise and public sectors. Exploitation could lead to unauthorized code execution within the browser context, potentially allowing attackers to bypass security controls, steal sensitive data, or move laterally within corporate networks. The vulnerability could also be leveraged for targeted attacks against high-value sectors such as finance, government, and critical infrastructure, where Firefox is commonly used. Given the browser’s role as a primary interface for web applications and email, exploitation could facilitate phishing campaigns or delivery of malware payloads. The potential for denial of service via crashes could disrupt business operations, especially in environments relying on web-based tools. Moreover, the vulnerability’s exploitation does not require user authentication but does require user interaction in the form of visiting a malicious or compromised website, which is a common attack vector. The impact is heightened by the fact that many organizations may not have updated to the latest Firefox ESR versions, leaving a large attack surface. The vulnerability could also affect remote workers using Firefox on personal or corporate devices, increasing the risk of widespread compromise.

Organizations should prioritize updating all Firefox installations to version 140 or later, or the corresponding ESR versions 115.25 or 128.12 and above, as soon as patches become available. Until updates are applied, organizations can implement network-level protections such as blocking access to known malicious domains and employing web filtering to restrict access to untrusted websites. Deploying endpoint detection and response (EDR) solutions with behavioral analytics can help identify exploitation attempts involving browser crashes or unusual memory activity. Administrators should enforce strict browser security configurations, including disabling or limiting font loading from untrusted sources if possible, and enabling sandboxing features to contain potential exploits. User education on avoiding suspicious links and websites remains critical. Additionally, monitoring security advisories from Mozilla and subscribing to vulnerability feeds will ensure timely awareness of patch releases and exploit developments. For high-security environments, consider using alternative browsers with different rendering engines until patches are confirmed deployed. Finally, incident response plans should be updated to include detection and mitigation steps for exploitation attempts related to this vulnerability.