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Fencer Intel
critical 10.0

CVE-2026-25641 json

SandboxJS has a sandbox escape via TOCTOU bug on keys in property accesses

published 9mo ago modified 4mo ago also EUVD-2026-5589 , GHSA-7x3h-rm86-3342

cvss
10.0
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

Summary

SandboxJS is a JavaScript sandboxing library. Prior to 0.8.29, there is a sandbox escape vulnerability due to a mismatch between the key on which the validation is performed and the key used for accessing properties. Even though the key used in property accesses is annotated as string, this is never enforced. So, attackers can pass malicious objects that coerce to different string values when used, e.g., one for the time the key is sanitized using hasOwnProperty(key) and a different one for when the key is used for the actual property access. This vulnerability is fixed in 0.8.29.

Patch / fix

  • npm @nyariv/sandboxjs 0.8.29
  • nyariv sandboxjs 0.8.29

Is CVE-2026-25641 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
total
Assessed
9mo ago

Exploit prediction

0.52% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/nyariv/SandboxJS/security/advisories/GHSA-7x3h-rm86-3342 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: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
NVD 3.1 9.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
npm @nyariv/sandboxjs
<0.8.29
0.8.29

Affected products

  • nyariv SandboxJS

Classification

Weakness
  • CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition
  • CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component

References

Sources

Fencer Intel 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.