Security Digest · Vulnerability record
CVE-2026-25520: @nyariv/sandboxjs has a Sandbox Escape issue
SandboxJS is a JavaScript sandboxing library.
CVSS 10.0 Critical EPSS 0.9% · p59
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.9%, percentile 59: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 59% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes
@nyariv/sandboxjs(npm) <= 0.8.28, fixed in 0.8.29. Check your lockfile, including transitive dependencies.
What it is
SandboxJS is a JavaScript sandboxing library. Prior to 0.8.29, The return values of functions aren't wrapped. Object.values/Object.entries can be used to get an Array containing the host's Function constructor, by using Array.prototype.at you can obtain the hosts Function constructor, which can be used to execute arbitrary code outside of the sandbox. This vulnerability is fixed in 0.8.29.
From the GitHub advisory
Summary
The return values of functions aren't wrapped. Object.values/Object.entries can be used to get an Array containing the host's Function constructor, by using Array.prototype.at you can obtain the hosts Function constructor, which can be used to execute arbitrary code outside of the sandbox.
Details
The return values of functions aren't wrapped, chaining function calls allows bypassing most validation/sanitization.
PoC
Weakness type: CWE-74.
Product: @nyariv/sandboxjs (npm) · Assigned by: GitHub_M · Published: 2026-02-06
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| npm | @nyariv/sandboxjs | <= 0.8.28 | 0.8.29 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| nyariv | SandboxJS | < 0.8.29 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 3.1 | 10 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H |
| GitHub | 3.1 | 10.0 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: changed (can affect other components)
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.89% probability of exploitation activity in the next 30 days; percentile 59.
Timeline
- — GitHub-reviewed advisory GHSA-58jh-xv4v-pcx4 published (critical)
- — CVE record last updated
- — CVE record published by GitHub_M
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-58jh-xv4v-pcx4 github.com
- CVE.org record CVE-2026-25520 cve.org
- NVD entry CVE-2026-25520 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com