Cyber Resilience

CVE-2026-25521

Locutus 2.0.12 – 2.0.39

Public PoC
Published
04 February 2026
Modified
15 July 2026
Patch / advisory
View advisory
CVSS Score v4 9.4
Click a component to see what it means
Raw vectorCVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0026 18th percentile
Risk Priority 37 floored blend · peak EPSS

Summary

CVE-2026-25521 is a critical-severity Prototype Pollution (CWE-1321) vulnerability in Locutus Locutus. Its CVSS base score is 9.4 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 18th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-6 (Least Privilege) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2026-25521 is a prototype pollution vulnerability (CWE-1321) affecting the Locutus JavaScript library, which ports standard libraries from other programming languages to JavaScript for educational purposes. The issue impacts versions from 2.0.12 up to but not including 2.0.39. Despite a prior fix that checked user input for forbidden keys, attackers can still pollute Object.prototype using a crafted input via String.prototype. Published on 2026-02-04, it carries a CVSS v3.1 base score of 8.8 (AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H).

A local attacker with low privileges can exploit this vulnerability with low complexity and no user interaction required. By supplying crafted input, they can modify Object.prototype, potentially leading to high impacts on confidentiality, integrity, and availability due to the changed scope.

The vulnerability is patched in Locutus version 2.0.39. Mitigation details are available in the patching commit at https://github.com/locutusjs/locutus/commit/042af9ca7fde2ff599120783e720a17f335bb01c and the GitHub security advisory at https://github.com/locutusjs/locutus/security/advisories/GHSA-rxrv-835q-v5mh.

OWASP Top 10 for Web (2025)

A08:2025 Software or Data Integrity Failures

EU & UK References

Vulnerability Data

Locutus brings stdlibs of other programming languages to JavaScript for educational purposes. In versions from 2.0.12 to before 2.0.39, a prototype pollution vulnerability exists in locutus. Despite a previous fix that attempted to mitigate prototype pollution by checking whether user…

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input contained a forbidden key, it is still possible to pollute Object.prototype via a crafted input using String.prototype. This issue has been patched in version 2.0.39.

CWE(s)
CWE-1321CWE-915

Related Threats

MITRE ATT&CK Enterprise Techniques

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1059 Command and Scripting Interpreter Execution
Adversaries may abuse command and script interpreters to execute commands, scripts, or binaries.
attack.mitre.org →
T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1098 Account Manipulation Persistence
Adversaries may manipulate accounts to maintain and/or elevate access to victim systems.
attack.mitre.org →
T1098.001 Additional Cloud Credentials Persistence
Adversaries may add adversary-controlled credentials to a cloud account to maintain persistent access to victim accounts and instances within the environment.
attack.mitre.org →
T1098.003 Additional Cloud Roles Persistence
An adversary may add additional roles or permissions to an adversary-controlled cloud account to maintain persistent access to a tenant.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-33994Same product: Locutus Locutus
CVE-2026-33993Same product: Locutus Locutus
CVE-2026-32304Same product: Locutus Locutus
CVE-2026-29091Same product: Locutus Locutus
CVE-2026-42044Shared CWE-1321, CWE-915
CVE-2026-42264Shared CWE-1321, CWE-915
CVE-2026-29063Shared CWE-1321, CWE-915
CVE-2026-42033Shared CWE-1321, CWE-915
CVE-2026-46625Shared CWE-1321, CWE-915
CVE-2026-33228Shared CWE-1321, CWE-915

Affected Assets

locutus
locutus
2.0.12 — 2.0.39

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V15.3.6

Mitigating Controls (NIST 800-53 r5) AI

AC-3 Access Enforcement good match

Enforces authorizations so that only permitted attributes may be modified on an object.

AC-6 Least Privilege good match

Limits the set of modifiable attributes a subject is authorized to touch.

SI-10 Information Input Validation good match

Validates incoming attribute names and values so that only explicitly allowed fields are accepted for update.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require input validation and safe property assignment to prevent prototype pollution.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.28 Secure coding mostly match
prevents

Secure coding standards explicitly forbid unsafe dynamic attribute assignment and require property allow-lists.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development catches prototype-pollution flaws before release.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle mandates input validation and object-handling controls that directly prevent prototype pollution.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly call for safeguards against unsafe object attribute manipulation.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles reduce the likelihood of prototype pollution through safe design patterns.

A.8.3 Information access restriction partial match
prevents

Information access restriction limits who can modify objects but does not address which attributes may be changed.

References