Prototype Pollution in Locutus
CVE-2026-25521
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 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.
Vulnerability class: Prototype Pollution
EPSS: 0.003 (17.8th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H.
Affected products
- Locutus
- Locutusjs Locutus — versions >= 2.0.12, < 2.0.39
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Exploit, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Frequently asked questions
- What is CVE-2026-25521?
- CVE-2026-25521 is a high-severity vulnerability in Locutus, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 8.8/10. Published 2026-02-04.
- How severe is CVE-2026-25521?
- High severity. CVSS v3 base score is 8.8 out of 10.