Critical severity9.8NVD Advisory· Published Jun 23, 2026· Updated Jul 7, 2026

CVE-2026-12866

Description

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.

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Affected products

Npm/Expr Evalinferred
Package: https://npmjs.com/package/expr-eval
Silentmatt/expr-evalllm-create

Patches

Vulnerability mechanics

References

github.com/silentmatt/expr-eval/blob/master/src/expression.js%23L55nvd
github.com/silentmatt/expr-eval/issues/292nvd
security.snyk.io/vuln/SNYK-JAVA-ORGWEBJARSNPM-17662018nvd
security.snyk.io/vuln/SNYK-JS-EXPREVAL-15054690nvd

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exploit	0.000
kev	0.000
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ransomware	0.000