CVE-2025-10532 is a vulnerability identified in Mozilla Firefox and Thunderbird, specifically affecting versions earlier than Firefox 143 and Firefox ESR 140.3. The root cause is incorrect boundary conditions in the JavaScript garbage collection (GC) component, categorized under CWE-754 (Improper Check for Unusual or Exceptional Conditions). This flaw can lead to memory safety issues, such as out-of-bounds reads or writes, which may allow an attacker to access or manipulate sensitive information within the browser's memory space. The vulnerability has a CVSS v3.1 base score of 6.5, indicating a medium severity level. The vector string (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N) shows that the attack can be performed remotely over the network without any privileges or user interaction, affecting confidentiality and integrity but not availability. No patches or exploit code are currently publicly available, and no known exploits have been reported in the wild. However, due to the nature of the flaw in the JavaScript GC, attackers could craft malicious web content or emails that trigger the vulnerability, potentially leading to information leakage or data manipulation within the browser or email client. The vulnerability affects multiple Mozilla products, including Firefox and Thunderbird, which are widely used across various sectors, including government, finance, and education, making it a relevant concern for organizations relying on these applications.

For European organizations, this vulnerability poses a risk primarily to confidentiality and integrity of data processed within Firefox and Thunderbird. Attackers exploiting this flaw could potentially access sensitive information such as session tokens, credentials, or email content, which could lead to further compromise or data breaches. Although the vulnerability does not impact availability, the ability to leak or alter data can undermine trust and compliance with data protection regulations such as GDPR. Organizations in sectors with high Firefox and Thunderbird usage—such as public administration, financial services, and academia—may face increased risk. The lack of required user interaction or privileges lowers the barrier for exploitation, increasing the threat surface. Additionally, the widespread use of these products in Europe means that a large number of endpoints could be vulnerable, amplifying potential impact. The absence of known exploits currently provides a window for proactive mitigation, but the medium severity rating suggests that timely patching is essential to prevent future exploitation.

European organizations should prioritize updating Mozilla Firefox and Thunderbird to versions 143 and ESR 140.3 or later as soon as official patches are released. Until patches are available, organizations can implement several practical mitigations: 1) Deploy network-level protections such as web filtering and intrusion detection systems to block or monitor suspicious JavaScript activity from untrusted sources. 2) Use browser security extensions that restrict or sandbox JavaScript execution, such as NoScript or uBlock Origin, to reduce exposure to malicious scripts. 3) Educate users about the risks of visiting untrusted websites or opening suspicious emails, even though no user interaction is required for exploitation, to reduce attack vectors. 4) Employ endpoint detection and response (EDR) solutions to monitor for anomalous behavior indicative of exploitation attempts. 5) Regularly audit and restrict browser extensions to minimize attack surface. 6) For organizations using Thunderbird, ensure email filtering and scanning solutions are up to date to detect potentially malicious content. These measures, combined with prompt patching, will significantly reduce the risk posed by this vulnerability.