CVE-2026-86083: n8n: Expression Sandbox Escape via Shared Builtin Tampering and Code-Printer Injection Leads to Code Execution

Two stages of expression code generation call the global JSON.stringify at generation time. The compiler uses it when printing synthetic string literals, and the isolate bridge uses it to put a timezone value into its per-evaluation wrapper. Because the call goes through global state, an expression that overwrites JSON.stringify can make later generated code contain attacker text. The patch renders both stages through a reference captured at module load.

The attacker is an authenticated user who can write expressions and has low privileges, with a present attack requirement in the CVSS 4.0 vector. The outcome is command execution in the n8n process, with high confidentiality, integrity and availability impact. That process holds stored credentials for connected services.

Only the legacy expression engine is vulnerable. The vm engine, the default on the patched releases, is not. So the risk is concentrated in older instances and those that set the legacy engine explicitly.

Affected: n8n before 1.123.76; 2.0.0 up to but not including 2.37.7; and 2.38.0 and 2.38.1, only when the legacy expression engine is in use. Check the engine setting N8N_EXPRESSION_ENGINE and the version:

n8n --version

Upgrade to n8n 1.123.76, 2.37.7 or 2.38.2, or later.

npm install -g [email protected]

n8n's temporary mitigations: set N8N_EXPRESSION_ENGINE=vm, restrict instance access to fully trusted users, and run the n8n process under a dedicated low-privilege OS account to limit the effect of command execution. These do not fully remediate the risk.

Search workflow expressions for assignments to JSON.stringify or other overwrites of built-in globals. Check which users edited workflows recently. On the host, look for unexpected child processes, outbound connections, or file writes from the n8n process, which a low-privilege OS account makes easier to spot.

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.