CVE-2026-34208
Published: 06 April 2026
Summary
CVE-2026-34208 is a critical-severity Protection Mechanism Failure (CWE-693) vulnerability in Nyariv Sandboxjs. Its CVSS base score is 10.0 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 49.7% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified are NIST 800-53 SC-4 (Information in Shared System Resources) and SC-50 (Software-enforced Separation and Policy Enforcement).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly mitigates the CVE by requiring timely patching of the SandboxJS library flaw, such as upgrading to version 0.8.36 to block constructor-based bypasses of global object protections.
Enforces software-based separation policies to isolate sandboxed JavaScript execution from host global objects, preventing unauthorized mutations via exposed constructors.
Prevents unauthorized modification of information residing in shared system resources like host global objects that persist mutations across SandboxJS instances.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The vulnerability directly enables privilege escalation by allowing arbitrary writes to host global objects from within the SandboxJS sandbox, bypassing isolation and persisting mutations across instances.
NVD Description
SandboxJS is a JavaScript sandboxing library. Prior to 0.8.36, SandboxJS blocks direct assignment to global objects (for example Math.random = ...), but this protection can be bypassed through an exposed callable constructor path: this.constructor.call(target, attackerObject). Because this.constructor resolves to the…
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internal SandboxGlobal function and Function.prototype.call is allowed, attacker code can write arbitrary properties into host global objects and persist those mutations across sandbox instances in the same process. This vulnerability is fixed in 0.8.36.
Deeper analysisAI
CVE-2026-34208 affects SandboxJS, an open-source JavaScript sandboxing library, in versions prior to 0.8.36. The vulnerability stems from inadequate protection against indirect mutations of host global objects. While SandboxJS blocks direct assignments to globals like Math.random, attackers can bypass this via an exposed callable constructor path: this.constructor.call(target, attackerObject). Here, this.constructor resolves to the internal SandboxGlobal function, and since Function.prototype.call is permitted, malicious code can arbitrarily write properties into the host environment's global objects.
Any attacker with code execution inside a SandboxJS sandbox can exploit this remotely over a network with low complexity, no privileges, and no user interaction required, as indicated by the CVSS 3.1 score of 10.0 (AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:L). Successful exploitation allows writing arbitrary properties to host global objects, with these mutations persisting across multiple sandbox instances in the same process. This grants high-impact confidentiality and integrity violations, plus low availability impact, potentially enabling privilege escalation, data exfiltration, or corruption of shared state in multi-tenant or sandboxed JavaScript environments.
The GitHub Security Advisory (GHSA-2gg9-6p7w-6cpj) confirms the issue and states that it is fixed in SandboxJS version 0.8.36. Security practitioners should upgrade to 0.8.36 or later, review sandbox usage for exposed constructor paths, and audit applications relying on SandboxJS for isolation in Node.js or browser contexts. The vulnerability maps to CWE-693 (Protection Mechanism Failure) and CWE-915 (Improperly Controlled Modification of Dynamically-Determined Object Attributes).
Details
- CWE(s)