Critical SandboxJS Sandbox Escape Enables Host Remote Code Execution
A critical vulnerability in the npm package @nyariv/sandboxjs allows attackers to escape the JavaScript sandbox and execute arbitrary code on the host system. The issue, tracked as CVE-2026-43898, affects all versions through 0.9.5 and has been rated CVSS 10.0. Public reporting and GitHub advisory coverage describe the flaw as a sandbox escape that can be triggered without credentials or user interaction, creating a path to full host takeover when applications use the library to process untrusted JavaScript.
The bug stems from improper exposure of internal callback functionality during function property access, including caller, callee, and arguments, enabling attackers to recover the host Function constructor and run arbitrary JavaScript or system commands. Separate advisory reporting also describes a sandbox escape caused by a TOCTOU bug in key handling during property access, underscoring broader weaknesses in the package's isolation model. Maintainers released 0.9.6 to block access to the dangerous properties, and organizations using SandboxJS are being urged to upgrade immediately or stop executing untrusted code with the library.
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How this story unfolded
3 events from the most recent confirmed update back to the earliest known activity.
SandboxJS 0.9.6 released to block dangerous property access
The vulnerability was fixed in version 0.9.6 by blocking access to the caller, callee, and arguments properties that enabled exploitation. Users were advised to upgrade immediately or stop processing untrusted JavaScript with the library.
Critical SandboxJS RCE flaw disclosed as CVE-2026-43898
A critical vulnerability in @nyariv/sandboxjs affecting all versions through 0.9.5 was publicly disclosed as CVE-2026-43898, with reports stating it enables sandbox escape and full remote code execution on the host without credentials or user interaction. Coverage also noted a proof-of-concept and technical details showing abuse of function property access to recover the host Function constructor.
SandboxJS TOCTOU sandbox escape advisory published
A GitHub security advisory was published for a SandboxJS sandbox escape caused by a TOCTOU bug involving keys in property accesses. The advisory documents a security issue affecting the nyariv/SandboxJS project.
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Critical SandboxJS Sandbox-Escape Vulnerabilities Enabling Host Code Execution
Multiple **critical vulnerabilities in *SandboxJS***—a JavaScript sandboxing library used to run untrusted code—were disclosed as enabling **sandbox escape and arbitrary code execution on the host**, with several issues scored **CVSS 10.0**. Reported flaws include **CVE-2026-25520**, **CVE-2026-25586**, **CVE-2026-25587**, and **CVE-2026-25641**, described as providing multiple paths to break out of SandboxJS’s isolation guarantees and take over the underlying runtime environment. Technical details published for **CVE-2026-25520** indicate that, prior to *SandboxJS* `0.8.29`, **function return values are not wrapped**, allowing attackers to use `Object.values()`/`Object.entries()` to obtain an array containing the host’s `Function` constructor (e.g., via `Array.prototype.at`), which can then be used to execute code outside the sandbox; the issue is fixed in `0.8.29` (with a referenced upstream commit and GitHub Security Advisory). Additional reported escape vectors include manipulation of supposedly safe prototypes (e.g., overwriting `Map.prototype.has` via a bug in the library’s `let` implementation) and a **host prototype pollution** condition tied to unsafe property-checking logic, collectively undermining the library’s core containment model.
Jun 29, 2026
SandboxJS Sandbox Escape via Host Prototype Pollution (CVE-2026-25881)
**CVE-2026-25881** is a critical sandbox-escape flaw in *SandboxJS* (`@nyariv/sandboxjs`) that allows sandboxed JavaScript to **mutate host built-in prototypes** (e.g., `Map.prototype`, `Set.prototype`) and cause persistent **host-side prototype pollution**. The issue stems from SandboxJS’s `isGlobal` protection mechanism: when a global prototype reference is placed into an **array literal** and then retrieved, the `isGlobal` “taint” is stripped, enabling direct prototype mutation from within the sandbox. The vulnerability affects versions **prior to 0.8.31** and is fixed in **0.8.31**; CVSS v3.1 is reported as `AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H` and the weakness is mapped to **CWE-1321**. Public reporting indicates a working **proof-of-concept (PoC)** is available demonstrating multiple exploitation scenarios, including adding attacker-controlled properties to host prototypes and overwriting built-in functions. While the sandbox escape itself is the core impact, **remote code execution is application-dependent**: if the host application later uses polluted properties in sensitive sinks (example gadget: `execSync(obj.cmd)`), an attacker can potentially execute system commands (e.g., `id`). Organizations using SandboxJS to run untrusted code should prioritize upgrading to **0.8.31** and review host code paths for dangerous use of object properties that could be influenced via prototype pollution.
Jun 29, 2026
Multiple Critical vm2 Sandbox Escapes Enable Host RCE in Node.js
A wave of disclosures has exposed multiple critical flaws in the Node.js sandbox library **vm2**, showing that untrusted JavaScript can break out of the sandbox and execute commands on the host. GitHub advisories describe several distinct escape paths affecting versions as old as `3.9.6` and, in some cases, up to `3.11.3`, including a breakout through Node.js `inspect`, a Promise species bypass that defeats an earlier patch, prototype pollution through vm2’s bridge to host intrinsic prototypes, and a `NodeVM` misconfiguration path where `nesting: true` lets code bypass `require: false` and load `vm2` recursively to reach modules such as `child_process`. Public proof-of-concepts show attackers recovering the host `process` object and invoking host commands, turning vm2 from a containment boundary into a route to full host compromise. Additional reporting and upstream changes indicate the problems are broader than a single bug. Semgrep documented a new sandbox escape, while vm2 maintainers added regression tests covering descriptor- and prototype-traversal techniques used to recover host constructors such as `Function`, `AsyncFunction`, and `GeneratorFunction`, as well as callback sanitization bypasses tied to Promise handling. A later roundup described five critical vulnerabilities with no practical configuration-based workaround for deployments that execute untrusted code, and urged upgrades to **vm2 `3.11.4` or later**. The advisory backlog on the project’s GitHub page shows a concentrated set of newly published sandbox escape, builtin bypass, and host code execution issues, underscoring that organizations relying on vm2 for isolation should treat affected environments as potentially compromised.
Jun 29, 2026