CVE-2025-5264 is a vulnerability identified in Mozilla Firefox and Thunderbird that stems from improper handling of newline characters in the 'Copy as cURL' feature. This feature allows users to copy HTTP requests as cURL commands for debugging or scripting purposes. The vulnerability occurs because newline characters are not sufficiently escaped, enabling an attacker to craft a malicious HTTP request that, when copied and executed by the user as a cURL command, can lead to local code execution on the user's system. The attack requires the victim to interact with the browser, specifically to use the 'Copy as cURL' functionality and then execute the copied command in a local shell environment. The vulnerability affects Firefox versions earlier than 139, Firefox ESR versions earlier than 115.24 and 128.11, and Thunderbird versions earlier than 139 and 128.11. The CVSS 3.1 base score is 4.8 (medium), reflecting the need for local access, low complexity, some privileges, and user interaction. The vulnerability is categorized under CWE-77 (Improper Neutralization of Special Elements used in a Command ('Command Injection')). No public exploits have been reported yet, and no patches are linked at the time of this report, indicating that mitigation primarily involves awareness and cautious user behavior until updates are released. The threat is significant because it can lead to execution of arbitrary commands on the victim's machine, potentially compromising local data or system integrity.

For European organizations, this vulnerability poses a risk primarily to end-user systems where Firefox or Thunderbird are used, especially in environments where users may copy and execute cURL commands for development, debugging, or automation tasks. Successful exploitation could lead to local code execution, allowing attackers to run arbitrary commands with the privileges of the user executing the command. This could result in unauthorized access to sensitive information, modification or deletion of files, or further lateral movement within a network if the compromised user has elevated privileges. The impact on confidentiality, integrity, and availability is moderate due to the requirement of user interaction and local execution. However, in high-security environments or critical infrastructure sectors, even local code execution can have significant consequences. The absence of known exploits in the wild reduces immediate risk but does not eliminate the potential for targeted attacks. Organizations with remote or hybrid workforces using these affected versions may face increased exposure if users are less supervised or trained on safe command execution practices.

1. Monitor Mozilla's official channels for patches addressing CVE-2025-5264 and apply updates promptly once available. 2. Until patches are released, educate users about the risks of executing copied commands from browsers, emphasizing verification before running any cURL commands obtained via 'Copy as cURL'. 3. Implement endpoint security solutions that can detect and block suspicious command-line activities, especially those involving cURL or shell command executions originating from user actions. 4. Restrict user privileges to the minimum necessary to reduce the impact of potential local code execution. 5. Use application whitelisting to prevent unauthorized execution of commands or scripts. 6. Encourage the use of browser extensions or configurations that limit or disable the 'Copy as cURL' feature if it is not required for business processes. 7. Conduct regular security awareness training focusing on social engineering and command execution risks. 8. For critical systems, consider network segmentation and endpoint monitoring to detect anomalous activities that could result from exploitation.