CVE Intelligence
Critical Injection exploit reference

CVE-2026-25520 — SandboxJS: sandbox escape via unwrapped function return values (CVE-2026-25520)

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.

Published Feb 6, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.9% (30-day exploitation probability)+9
  • Technical severity (critical)+10
  • CISA SSVC: exploitation "poc"+5
  • Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.89%
ahead of 59% of scored CVEs · Oct 14, 2026
Affects
Nyariv
Sandboxjs
CVSS base
10.0
Critical · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
Proof of concept
none · proof-of-concept · active
Automatable
Yes
can an attacker script the kill-chain steps
Technical impact
Total
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented patch — github.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Nyariv Sandboxjs).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. Search available logs for exploit probes matching the vulnerability class (injection), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Nyariv Sandboxjs < 0.8.29 Vulnerable NIST National Vulnerability Database
Nyariv Sandboxjs version < 0.8.29 Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
10.0 CVSS 3.1 Critical 3.9 6.0 security-advisories@github.com via NIST National Vulnerability Database
10.0 CVSS 3.1 Critical — — GitHub_M via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H (score shown at the top: security-advisories@github.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-74 · Injection

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.89%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Look for parameters with command/query metacharacters and unexpected child processes of the service.
web/proxy/WAF logsnetwork IDS/IPSapplication logsendpoint telemetry (EDR)

Analysis and videos

CVE-2026-25520: SandboxJS: sandbox escape via unwrapped function return values
CVE-2026-25520 affects SandboxJS versions prior to 0.8.29, where function return values are not wrapped, allowing host objects to be reached from inside the sandbox. The record describes a path to run arbitrary code outside the sandbox, and it is fixed in 0.8.29. The CVSS 3.1 base score recorded is 10.0 (critical), and the CISA KEV catalog does not list it.

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · nyariv/sandboxjs
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Fix documented
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 10.0
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVE published
    Feb 6, 2026 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

2 on the record

Elsewhere on this site

Nyariv
every CVE for this vendor
Injection
same class
CWE-74
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-43898 SandboxJS: Sandbox escape via Function.caller leakage of internal call op May 28, 2026
  • CVE-2026-34208 SandboxJS: Sandbox integrity escape Apr 6, 2026
  • CVE-2026-34211 SandboxJS: Stack overflow DoS via deeply nested expressions in recursive descent parser Apr 6, 2026
  • CVE-2026-34217 SandboxJS has a Sandbox Escape via Prop Object Leak in New Handler Apr 6, 2026
  • CVE-2026-32723 SandboxJS timers have an execution-quota bypass (cross-sandbox currentTicks race) Mar 18, 2026
  • CVE-2026-26954 SandboxJS has a Sandbox Escape Mar 13, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-25520 is "SandboxJS: sandbox escape via unwrapped function return values (CVE-2026-25520)", rated Critical. It affects Sandboxjs (Nyariv); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 10.0 describes technical severity. EPSS 0.89% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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