3.7 Low

i18next-http-backend: Query-parameter injection through & and = in lng when loadPath/addPath puts {{lng}} in the query string

CVE-2026-118258

Summary The URL-segment check added for GHSA-q89c-q3h5-w34g blocks ?, #, %, :, / and @ in lng, but not & or =, and the checked value is inserted into the URL without encoding. The README documents a multiload loadPath of the form /locales/resources.json?lng=de+en&ns=ns1+ns2. With a template like that, an attacker who controls the language value can add or override query parameters on the request the backend sends. By default the language comes from ?lng=, a cookie or Accept-Language. This is the "query-string injection" impact described in GHSA-q89c; only the ? form was closed. Server side (Express + i18next-http-middleware, default options), GET /?lng=de%26ns%3Dprivate%26admin%3Dtrue makes the application request …?lng=de&ns=private&admin=true&ns=common from its own translations API. Details The checks are in lib/utils.js. The base check (https://github.com/i18next/i18next-http-backend/blob/v4.0.3/lib/utils.js#L26-L44) rejects: empty or >128-character values and prototype keys; .. and \; /[?#%:\s]/; control characters. isSafeLangUrlSegment (https://github.com/i18next/i18next-http-backend/blob/v4.0.3/lib/utils.js#L51-L55) adds only / and @. Neither function rejects & or =. js if…

Assessment

CVSS: 3.7 (v3.1)
Severity: Low
EPSS: 0.0028% chance of exploitation in the next 30 days
Known exploited: Not listed in CISA KEV
Exploit availability: Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
Published: 28 October 2026
Last updated: 28 October 2026
Affected: npm · i18next-http-backend
Weakness: CWE-74

CVSS vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

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