Prototype Pollution in Nyariv Sandboxjs
CVE-2026-25881
SandboxJS is a JavaScript sandboxing library. Prior to 0.8.31, a sandbox escape vulnerability allows sandboxed code to mutate host built-in prototypes by laundering the isGlobal protection flag through array literal intermediaries. When a global prototype reference (e.g., Map.prototype, Set.prototype) is placed into an array and retrieved, the isGlobal taint is stripped, permitting direct prototype mutation from within the sandbox. This results in persistent host-side prototype pollution and may enable RCE in applications that use polluted properties in sensitive sinks (example gadget: execSync(obj.cmd)). This vulnerability is fixed in 0.8.31.
Vulnerability class: Prototype Pollution
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.0 (Critical). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.007 (49.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 49th percentile — 49.2% 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: 0.007 · change: +0.001
Affected products
- Nyariv Sandboxjs — versions < 0.8.31
Weakness classification (CWE)
References
- github.com/nyariv/SandboxJS/security/advisories/GHSA-ww7g-4gwx-m7wj (Exploit, Mitigation, Vendor Advisory)
- github.com/nyariv/SandboxJS/commit/f369f8db26649f212a6a9a2e7a1624cb2f705b53 (Patch)
Frequently asked questions
- What is CVE-2026-25881?
- CVE-2026-25881 is a critical-severity vulnerability in Nyariv Sandboxjs, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 9.0/10. Published 2026-02-09.
- How severe is CVE-2026-25881?
- Critical severity. CVSS v3 base score is 9.0 out of 10.