CVE-2025-5265 is a vulnerability identified in Mozilla Firefox for Windows and Thunderbird clients affecting versions prior to Firefox 139 and ESR versions 115.24 and 128.11, as well as Thunderbird versions prior to 139 and 128.11. The root cause is insufficient escaping of the ampersand character in the 'Copy as cURL' feature, which is designed to allow users to copy HTTP requests as cURL commands for debugging or testing purposes. An attacker can exploit this flaw by tricking a user into copying and executing a maliciously crafted cURL command that includes specially crafted ampersand characters. Because the ampersand is a command separator in Windows command shells, improper escaping can lead to execution of arbitrary commands on the local system. This results in local code execution with the privileges of the user running the command. The attack requires the user to interact by copying and executing the command, and the attacker must convince the user to perform this action, typically through social engineering or phishing. The vulnerability is classified under CWE-77 (Improper Neutralization of Special Elements used in a Command), indicating command injection risks. The CVSS v3.1 base score is 4.8 (medium), reflecting the need for local access, user interaction, and limited privileges. No public exploits or active exploitation have been reported to date. This vulnerability affects confidentiality, integrity, and availability by enabling arbitrary code execution, potentially allowing attackers to steal data, modify system settings, or disrupt operations. However, the scope is limited to Windows users of affected Firefox and Thunderbird versions who execute malicious commands. Mozilla has not yet published patches but is expected to do so promptly.

For European organizations, this vulnerability poses a moderate risk primarily to Windows desktop environments where Firefox or Thunderbird are used. Successful exploitation could lead to local code execution, enabling attackers to gain unauthorized access to sensitive data, install malware, or disrupt user systems. This could impact confidentiality by exposing sensitive information, integrity by allowing unauthorized modifications, and availability by causing system instability or denial of service. The requirement for user interaction and local execution reduces the risk of widespread automated attacks but increases the threat from targeted phishing or social engineering campaigns. Organizations with large numbers of Windows users relying on Firefox or Thunderbird for email and web browsing are at higher risk. This includes sectors such as government, finance, healthcare, and critical infrastructure where data sensitivity and regulatory compliance are paramount. The vulnerability could also be leveraged as a foothold for further lateral movement within networks if attackers gain initial access through compromised endpoints. Given the medium severity and the lack of known exploits, the immediate impact is limited but warrants proactive mitigation to prevent exploitation.

1. Apply official patches from Mozilla as soon as they are released to address the vulnerability. 2. Until patches are available, consider disabling or restricting the 'Copy as cURL' feature in Firefox and Thunderbird through configuration policies or extensions to prevent misuse. 3. Educate users about the risks of executing commands copied from untrusted sources, emphasizing caution with commands involving cURL or shell execution. 4. Implement endpoint protection solutions that can detect and block suspicious command execution patterns, especially those involving command injection or unusual shell commands. 5. Use application whitelisting to prevent unauthorized execution of commands or scripts on Windows systems. 6. Monitor logs and endpoint telemetry for signs of suspicious activity related to command execution or user behavior anomalies. 7. Encourage the use of least privilege principles to limit user permissions, reducing the impact of any local code execution. 8. Conduct phishing awareness training to reduce the likelihood of users falling victim to social engineering attempts that could lead to exploitation.