SandboxJS: Sandbox integrity escape

published 2026-04-03 7 mo ago modified 2026-10-26 13 d ago also EUVD-2026-19297 , GHSA-2gg9-6p7w-6cpj

cvss: 10.0; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.6%; EPSS 0.6% chance of exploitation in 30 days, percentile 48%
public exploits: 0; none known

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 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.

Patch / fix

fixed in 2

npm @nyariv/sandboxjs 0.8.36
nyariv sandboxjs 0.8.36

CISA SSVC

Exploitation: Proof of concept is public
Automatable: yes
Technical impact: total
Assessed: 7 mo ago (2026-04-06)

Exploit prediction

0.58% chance of exploitation in the next 30 days, higher than 48% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/nyariv/SandboxJS/security/advisories/GHSA-2gg9-6p7w-6cpj referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	10.0	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:L
GitHub	3.1	10.0	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:L
NVD	3.1	10.0	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Affected packages

ecosystem	package	affected	fixed in
npm	@nyariv/sandboxjs	<0.8.36	0.8.36

Affected products

nyariv SandboxJS

Classification

Weakness

CWE-693 Protection Mechanism Failure
CWE-915 Improperly Controlled Modification of Dynamically-Determined Object Attributes

References

github.com /nyariv/SandboxJS/security/advisories/GHSA-2gg9-6p7w-6cpj
web, exploit, vendor-advisory
nvd.nist.gov /vuln/detail/CVE-2026-34208
advisory
github.com /nyariv/SandboxJS
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.

Summary