CVE-2026-86083 Overview
n8n is an open source workflow automation platform used to build and run automated pipelines. CVE-2026-86083 is a code injection vulnerability [CWE-94] in the legacy expression engine that allows attacker-controlled JavaScript to be embedded into generated source. The engine calls the mutable global JSON.stringify while printing synthetic string literals and interpolating timezone data. An expression can replace JSON.stringify, causing later generated source to include executable attacker-controlled code. The issue affects n8n versions prior to 1.123.76, 2.37.7, and 2.38.2. The vm expression engine is not affected.
Critical Impact
An authenticated user able to submit expressions can achieve arbitrary code execution within the n8n expression runtime, compromising workflow confidentiality, integrity, and availability.
Affected Products
- n8n versions prior to 1.123.76
- n8n versions prior to 2.37.7
- n8n versions prior to 2.38.2
Discovery Timeline
- 2026-09-08 - CVE-2026-86083 published to NVD
- 2026-09-09 - Last updated in NVD database
Technical Details for CVE-2026-86083
Vulnerability Analysis
The legacy expression engine in n8n generates JavaScript source text at runtime to evaluate user-supplied expressions. During generation, the engine invokes the global JSON.stringify function to serialize synthetic string literals and timezone metadata. Because JSON.stringify is a mutable global reference, an expression evaluated earlier can reassign it to an attacker-controlled function. Subsequent source generation then substitutes attacker output in place of properly escaped string literals. The result is injection of executable JavaScript into the generated program, which the runtime later evaluates.
The vulnerable code-generation paths are located in packages/@n8n/expression-runtime/src/bridge/isolated-vm-bridge.ts and packages/@n8n/tournament/src/ExpressionBuilder.ts. The vm expression engine follows a different code path and is not affected.
Root Cause
The root cause is unsafe reliance on a mutable global (JSON.stringify) inside a code-generation routine. The engine assumes the global will always return a properly quoted JSON string. When an earlier expression overwrites the global, the assumption breaks and the generated source no longer contains safely encoded literals. This is a classic improper control of generation of code [CWE-94] pattern combined with prototype and global-object tampering.
Attack Vector
Exploitation requires an authenticated user with permission to author or submit expressions in a workflow. The attacker first evaluates an expression that reassigns JSON.stringify to a function returning attacker-controlled text. A second expression, or continued execution of the same workflow, then triggers code generation that inlines the malicious return value directly into the compiled source. The runtime executes the injected code with the privileges of the expression engine. See the GitHub Security Advisory GHSA-6xcw-7xm6-48c6 for the vendor's technical description.
Detection Methods for CVE-2026-86083
Indicators of Compromise
- Workflow expressions containing assignments to global built-ins such as JSON.stringify, JSON.parse, or other prototype-level properties.
- Unexpected outbound network connections, file writes, or child process creation originating from the n8n service account.
- Newly created or modified workflows containing obfuscated string concatenation or unusual timezone parameter values.
Detection Strategies
- Audit workflow definitions and expression payloads for references to mutable globals being reassigned.
- Inspect n8n audit logs for expression authoring or edits performed by low-privilege accounts prior to anomalous runtime behavior.
- Correlate n8n process telemetry with unexpected shell, network, or filesystem activity that deviates from baseline workflow behavior.
Monitoring Recommendations
- Enable verbose logging on the n8n expression runtime and forward logs to a centralized SIEM for retention and analysis.
- Monitor the n8n host for process lineage anomalies, such as the Node.js runtime spawning shells or interpreters.
- Alert on newly installed n8n versions that do not match the patched releases 1.123.76, 2.37.7, or 2.38.2.
How to Mitigate CVE-2026-86083
Immediate Actions Required
- Upgrade n8n to 1.123.76, 2.37.7, or 2.38.2 depending on the deployed release track.
- Restrict workflow authoring and expression-editing permissions to trusted operators only.
- Review recently created or modified workflows for expressions that manipulate global objects.
Patch Information
The vendor has released fixed versions n8n@1.123.76, n8n@2.37.7, and n8n@2.38.2. The patches remove reliance on the mutable JSON.stringify global during source generation. Administrators should apply the update that matches their release channel and restart the n8n service.
Workarounds
- Switch execution to the vm expression engine, which is not affected by this issue.
- Limit n8n account provisioning so only vetted users can create or modify workflows and expressions.
- Isolate the n8n service on a dedicated host with egress filtering to contain the impact of any successful code execution.
# Upgrade example using npm
npm install -g n8n@1.123.76
# Verify installed version
n8n --version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
