CVE intelligence and bounded remediation
CVE-2026-12866 — All versions of the package expr-eval are vulnerable to Code Execution via the toJSFunction() API
All versions of the package expr-eval are vulnerable to Code Execution via the toJSFunction() API. An attacker can execute arbitrary JavaScript by supplying crafted expressions that are compiled into native code using new Function(). Because user-controlled expressions are transformed directly into executable JavaScript, attackers can escape the intended expression sandbox and run arbitrary code within the application's context.
- Severity
- Critical
- CVSS
- 9.8 (3.1)
- Published
- 2026-06-23
- CISA KEV
- Not currently listed
- Ecosystem
- javascript/npm
- Weaknesses
- CWE-94
Affected products
No browser-safe affected-product rows are available.
Matched remediation archetype
Command, code, expression, and template injection
This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.
Check exposure
- Trace untrusted values to process execution, interpreters, evaluators, template engines, dynamic imports, and administrative scripting features.
- Determine whether the affected path is reachable across each trust boundary and which service account or host privilege it inherits.
- Review configuration for optional execution features, unsafe compatibility modes, and shell invocation.
Remediate safely
- Replace string-built commands or evaluated code with fixed operations and structured argument APIs that do not invoke a shell.
- Use strict allowlists for operation identifiers and reject unexpected input before it reaches any interpreter.
- Update the affected component and add inert regression tests covering metacharacters, encoding variants, and alternate request paths.
Authoritative sources
Complete CVE record and remediation plan
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