A prototype pollution flaw (CWE‑488) is present in the Merge node’s SQL Query mode. Prior to version 2.25.7 and 2.26.2, an authenticated user with permission to create or modify workflows could pollute the sandbox used by that node. Because the sandbox context is cached and reused across all workflow executions on the instance, prototype mutations introduced by a user’s workflow persist into subsequent Merge SQL executions belonging to other users or projects. This allows a low‑privileged attacker to intercept workflow data processed by other users on the same instance, leading to confidential information leakage across users. The issue only affects multi‑user n8n instances where multiple users have permission to create and execute workflows that contain the Merge node in SQL Query mode.

All n8n installations running versions earlier than 2.25.7 or 2.26.2 on a multi‑user deployment are affected. Single‑user or single‑user‑mode instances are not impacted.

The vulnerability is rated CVSS 6, indicating moderate severity. EPSS is not available and the flaw is not listed in CISA KEV, suggesting it is not known to have been widely exploited. Exploitation requires an authenticated user with workflow creation or modification rights, so the attack surface is limited to the same n8n instance. An attacker can use the polluted sandbox to read data belonging to other users breach.