Prototype pollution and path traversal in i18next-http-middleware via user-controlled language and namespace parameters

published 2026-04-22 6 mo ago modified 2026-10-26 13 d ago also EUVD-2026-28792 , GHSA-5fgg-jcpf-8jjw

cvss: 8.6; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 24%
public exploits: 0; none known

18next-http-middleware is a middleware to be used with Node.js web frameworks like express or Fastify and also for Deno. Versions prior to 3.9.3 allow an unauthenticated HTTP client to pollute Object.prototype in the Node.js process hosting the middleware, via two unvalidated entry points that reach internal object-key writes: getResourcesHandler and missingKeyHandler. This can break authorisation checks (if (user.isAdmin) returning true for any user), cause type-confusion DoS, and depending on downstream code it can be chained into RCE.

Patch / fix

fixed in 2

npm i18next-http-middleware 3.9.3
i18next i18next-http-middleware 3.9.3

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: partial
Assessed: 6 mo ago (2026-05-08)

Exploit prediction

0.31% chance of exploitation in the next 30 days, higher than 24% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	8.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L
GitHub	3.1	8.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

Affected packages

ecosystem	package	affected	fixed in
npm	i18next-http-middleware	<3.9.3	3.9.3

Affected products

i18next i18next-http-middleware

Classification

Weakness

CWE-22 Improper Limitation of a Pathname to a Restricted Directory
CWE-1321 Improperly Controlled Modification of Object Prototype Attributes

References

Sources

Fencer Vulns 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.

Summary