CVE-2025-4089 is a vulnerability identified in Mozilla Firefox and Thunderbird versions prior to 138, specifically affecting the "copy as cURL" feature. This feature allows users to copy HTTP requests as cURL command-line instructions for debugging or replication purposes. The vulnerability arises due to insufficient escaping of special characters within this feature, which can be exploited by an attacker to inject malicious commands. When a user executes the copied cURL command in a terminal or command prompt, the injected code can be executed locally on the user's system. This represents a local code execution (LCE) vulnerability, where the attacker must first trick the user into copying and running the crafted cURL command. The vulnerability is classified under CWE-77 (Improper Neutralization of Special Elements used in a Command), indicating command injection risks. The CVSS 3.1 base score is 5.1 (medium severity), reflecting that the attack vector is local (AV:L), requires low attack complexity (AC:L), no privileges (PR:N), and no user interaction (UI:N) once the command is executed. However, the initial step requires the user to perform the copy and execute the command, which is a form of user interaction. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability impacts confidentiality and integrity by allowing arbitrary code execution, but does not affect availability directly. Since the attack requires local execution of the crafted command, remote exploitation is not feasible without social engineering to convince the user to run the malicious command.

For European organizations, this vulnerability poses a risk primarily through social engineering attacks targeting users who utilize the "copy as cURL" feature for legitimate debugging or development tasks. Successful exploitation could lead to local compromise of user machines, potentially allowing attackers to execute arbitrary code, steal sensitive information, or move laterally within internal networks. Organizations with developers, IT staff, or security analysts frequently using Firefox or Thunderbird for web debugging are at higher risk. The impact includes potential data breaches, espionage, or disruption of internal systems if attackers gain footholds via compromised endpoints. Since Firefox and Thunderbird are widely used across Europe, especially in government, finance, and technology sectors, the vulnerability could be leveraged in targeted attacks against high-value entities. However, the requirement for user execution of the malicious command limits mass exploitation, making it more suitable for targeted spear-phishing or social engineering campaigns. The medium CVSS score reflects moderate risk, but the potential for local code execution elevates the threat in environments with sensitive data or critical infrastructure.

1. Educate users, especially developers and IT personnel, about the risks of blindly executing copied commands from untrusted sources, emphasizing caution when using the "copy as cURL" feature. 2. Implement strict endpoint security controls such as application whitelisting and behavior monitoring to detect and block unauthorized command executions. 3. Employ sandboxing or containerization for running command-line tools to limit the impact of potential code execution. 4. Monitor internal communications and phishing attempts that may attempt to trick users into executing malicious cURL commands. 5. Encourage rapid updating to Firefox and Thunderbird version 138 or later once patches are released to address this vulnerability. 6. Where possible, restrict use of the "copy as cURL" feature to trusted users or disable it temporarily in high-risk environments until a patch is available. 7. Use endpoint detection and response (EDR) solutions to identify suspicious command-line activity related to cURL or shell command injections. 8. Review and harden user privilege levels to minimize the impact of local code execution, ensuring users operate with least privilege.