CVE-2026-25520: nyariv sandboxjs sandbox escape to RCE

CVE-2026-25520 · Severity: low · CVSS 3.1 · Published 2026-02-05

SandboxJS is a JavaScript library used to safely execute untrusted code in an isolated sandbox environment. A critical flaw allows attackers to escape the sandbox and execute arbitrary system commands with full privileges on the host machine. This breaks the security guarantees of the sandboxing mechanism entirely, allowing anyone running untrusted code through this library to take complete control of the affected system.

Technologies: @nyariv/sandboxjs (npm), Nyariv Sandboxjs. Vendors: npm, Nyariv.

Quick answers

Is CVE-2026-25520 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-25520 being exploited in the wild.
How severe is CVE-2026-25520?
Low severity, with a CVSS score of 3.1, published 5 February 2026.
Which products and versions are affected?
@nyariv/sandboxjs (npm) SEMVER:introduced=0,fixed=0.8.29; Nyariv Sandboxjs <=0.8.28.
Is there a fix for CVE-2026-25520?
Yes. @nyariv/sandboxjs (npm): upgrade to 0.8.29 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-25520 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-25520?
Check whether you run @nyariv/sandboxjs (npm) or Nyariv Sandboxjs at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • @nyariv/sandboxjs (npm): upgrade to 0.8.29 or later
    npm install @nyariv/sandboxjs@0.8.29

Technical details

The vulnerability is a sandbox escape caused by improper wrapping of function return values. When functions return objects, those objects retain references to the host environment's Function constructor. An attacker can chain Object.values() or Object.entries() with Array.prototype.at() to extract the host's Function constructor, then use it to execute arbitrary code via the Function constructor's call signature. No authentication or user interaction is required; the attack is triggered simply by compiling and running malicious code through the sandbox. The root cause is insufficient isolation of return values from internal sandbox functions. A patch is available in version 0.8.29 which hardens return value wrapping to prevent constructor access.

Affected products

  • nyariv sandboxjs <=0.8.28

Identifiers

  • CVE-2026-25520
  • GHSA-58jh-xv4v-pcx4

Timeline

  • 2026-02-05: disclosed
  • 2026-02-05: patched: Fixed in version 0.8.29

References

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