Attack Chain

1. An attacker deploys a Node.js application using Node.js 25.x with the --permission flag and intentionally omits the --allow-net flag to restrict network access.
2. The application leverages the net module or a similar mechanism to create a Unix Domain Socket server. This operation should, in theory, be blocked by the permission model due to the missing --allow-net flag, but due to the vulnerability, the UDS server is created successfully.
3. The attacker specifies a path for the UDS that allows other processes on the system to connect to it.
4. A separate, possibly malicious, process on the same host connects to the created UDS. This process could be under the attacker’s control or a compromised service.
5. The attacker’s application and the connecting process establish a communication channel over the UDS.
6. The attacker uses this channel to send commands, data, or other instructions between the two processes, bypassing the intended network restrictions.
7. The receiving process executes the commands or processes the data received, potentially leading to privilege escalation, data leakage, or other malicious activities.
8. The attacker achieves their objective, such as gaining unauthorized access to system resources or compromising the integrity of the receiving process.

Impact

Successful exploitation of CVE-2026-21711 can lead to a bypass of intended network isolation in Node.js applications. This may allow unauthorized processes to communicate with and potentially control isolated applications, leading to privilege escalation, data leakage, or other forms of compromise. The vulnerability affects Node.js 25.x processes utilizing the permission model. The number of affected installations is unknown, but the impact is potentially significant for environments relying on the permission model to restrict network access and isolate applications.

Recommendation

• Upgrade to a patched version of Node.js that addresses CVE-2026-21711 once available.
• Deploy the Sigma rules provided below to detect potential exploitation attempts within your environment, focusing on process creation events when the --permission flag is enabled.
• Monitor Node.js processes for suspicious UDS creation and connection activity using the network_connection log source.
• Review and harden the permission configurations of Node.js applications to prevent unintended access to sensitive resources.