What is CVE-2026-34208?

CVE-2026-34208 is a critical-severity vulnerability in Nyariv Sandboxjs, classified under Protection Mechanism Failure. CVSS score: 10.0/10. Published 2026-04-06.

How severe is CVE-2026-34208?

Critical severity. CVSS v3 base score is 10.0 out of 10.

Vulnerability in Nyariv Sandboxjs

CVE-2026-34208

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.

Published 2026-04-06 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 10.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:L.

EPSS exploit prediction

EPSS: 0.006 (46.8th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 47th percentile — 46.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: +0.000

Affected products

Nyariv Sandboxjs — versions < 0.8.36

Weakness classification (CWE)

References

github.com/nyariv/SandboxJS/security/advisories/GHSA-2gg9-6p7w-6cpj (Exploit, Vendor Advisory)

Frequently asked questions

What is CVE-2026-34208?: CVE-2026-34208 is a critical-severity vulnerability in Nyariv Sandboxjs, classified under Protection Mechanism Failure. CVSS score: 10.0/10. Published 2026-04-06.
How severe is CVE-2026-34208?: Critical severity. CVSS v3 base score is 10.0 out of 10.