n8n: Expression Sandbox Escape via Shared Builtin Tampering and Code-Printer Injection Leads to Code Execution

Impact

Two stages of expression code generation built source text by calling the global JSON.stringify at generation time: the compiler when printing synthetic string literals, and the isolate bridge when interpolating a timezone value into its per-evaluation wrapper. An expression that replaced that global therefore changed the code that was subsequently generated and executed, turning literal data into executable source. The patch renders both code-generation stages through a reference captured at module load, so a later change to global state cannot alter the generated source.

This vulnerability only affects instances running the legacy expression engine. The vm expression engine, which is the default on the patched releases, is not affected.

Patches

The issue has been fixed in n8n versions 1.123.76, 2.37.7, and 2.38.2. Users should upgrade to one of these versions or later to remediate the vulnerability.

Workarounds

If upgrading is not immediately possible, administrators should consider the following temporary mitigations:

• Set the environment variable N8N_EXPRESSION_ENGINE=vm to switch to the vm expression engine, which is not affected by this vulnerability.
• Restrict n8n instance access to fully trusted users only.
• Ensure the n8n process runs under a dedicated low-privilege OS user account to limit the impact of any command execution.

These workarounds do not fully remediate the risk and should only be used as short-term mitigation measures.