CVE-2025-5262 is a high-severity vulnerability identified in the libvpx encoder component used within Mozilla Thunderbird, specifically affecting versions prior to 139 and 128.11. The flaw is a double-free vulnerability occurring in the function vpx_codec_enc_init_multi, which is responsible for initializing the encoder for WebRTC video streams. The issue arises after a failed memory allocation during encoder initialization, where the code erroneously attempts to free the same memory region twice. This double-free condition can lead to memory corruption, which in turn may cause application crashes or potentially allow an attacker to execute arbitrary code. The vulnerability does not require any privileges or user interaction to be exploited, and it is remotely exploitable over the network since Thunderbird processes WebRTC streams that can be triggered by receiving specially crafted data. The CVSS v3.1 base score of 7.5 reflects the high impact on availability due to potential crashes, with no direct impact on confidentiality or integrity. Although no known exploits are currently reported in the wild, the nature of the vulnerability and its presence in a widely used email client with integrated WebRTC capabilities make it a significant risk. The vulnerability is classified under CWE-415 (Double Free), a common memory management error that can be leveraged for exploitation in complex ways depending on the memory layout and environment.

For European organizations, the impact of CVE-2025-5262 can be substantial, especially for those relying on Mozilla Thunderbird as a primary email client integrated with WebRTC functionalities for communication. Successful exploitation could lead to denial of service through application crashes, disrupting email and real-time communication workflows. More critically, if exploited for arbitrary code execution, attackers could gain control over affected systems, potentially leading to data breaches, lateral movement within networks, or deployment of malware. Given Thunderbird's use in both private and enterprise environments, this vulnerability could affect sensitive communications and data integrity. The lack of required privileges or user interaction lowers the barrier for attackers, increasing the risk of automated or targeted attacks. European organizations in sectors such as finance, government, healthcare, and critical infrastructure, which often use Thunderbird for secure communications, could face operational disruptions and increased exposure to cyber espionage or ransomware attacks if this vulnerability is exploited.

To mitigate CVE-2025-5262, European organizations should prioritize updating Mozilla Thunderbird to versions 139 or later, or at least 128.11 or later, where the vulnerability has been addressed. In the absence of an immediate patch, organizations should consider disabling WebRTC functionality within Thunderbird to prevent triggering the vulnerable code path. Network-level controls such as filtering or blocking suspicious WebRTC traffic can reduce exposure. Employing application sandboxing or running Thunderbird with least privilege can limit the impact of potential exploitation. Monitoring Thunderbird process crashes and unusual behavior can provide early detection of exploitation attempts. Additionally, organizations should ensure that endpoint protection solutions are up to date and capable of detecting exploitation techniques related to memory corruption. Regular security awareness training for users to recognize phishing or malicious email attachments that could trigger WebRTC streams is also recommended. Finally, maintaining robust backup and incident response plans will help mitigate the impact if exploitation occurs.