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

n8n is an open source workflow automation platform. Prior to 1.123.76, 2.37.7, and 2.38.2, the legacy expression engine generated source text by calling the mutable global JSON.stringify while printing synthetic string literals and interpolating timezone data. An expression could replace JSON.stringify and cause later generated source to contain executable attacker-controlled code. The affected code-generation paths include packages/@n8n/expression-runtime/src/bridge/isolated-vm-bridge.ts and packages/@n8n/tournament/src/ExpressionBuilder.ts, and the issue does not affect the vm expression engine. This issue is fixed in versions 1.123.76, 2.37.7 and 2.38.2.

n8n is an open source workflow automation platform. Prior to 1.123.76, 2.37.7, and 2.38.2, the legacy expression engine generated source text by calling the mutable global JSON.stringify while printing synthetic string literals and interpolating timezone data. An expression could replace JSON.stringify and cause later generated source to contain executable attacker-controlled code. The affected code-generation paths include packages/@n8n/expression-runtime/src/bridge/isolated-vm-bridge.ts and packages/@n8n/tournament/src/ExpressionBuilder.ts, and the issue does not affect the vm expression engine. This issue is fixed in versions 1.123.76, 2.37.7 and 2.38.2.

n8n is an open source workflow automation platform. Prior to 1.123.76, 2.37.7, and 2.38.2, the legacy expression engine generated source text by calling the mutable global JSON.stringify while printing synthetic string literals and interpolating timezone data. An expression could replace JSON.stringify and cause later generated source to contain executable attacker-controlled code. The affected code-generation paths include packages/@n8n/expression-runtime/src/bridge/isolated-vm-bridge.ts and packages/@n8n/tournament/src/ExpressionBuilder.ts, and the issue does not affect the vm expression engine. This issue is fixed in versions 1.123.76, 2.37.7 and 2.38.2.

## 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.