CVE-2026-118258 in i18next-http-backend
Summary
by MITRE • 10/28/2026
i18next-http-backend is a backend layer for i18next that loads translation resources in Node.js, browsers, and Deno. Prior to 4.0.4, interpolateUrl inserts unencoded language and namespace values into loadPath or addPath templates without rejecting ampersand (&), equals (=), or semicolon (;) query separators. When a template places lng or ns in the query string and an attacker controls that value, the attacker can add or override parameters on browser or server-side translation requests, potentially exposing other namespaces or tenants or changing backend behavior through the application's network position and credentials. This vulnerability is the result of an incomplete fix for CVE-2026-41691. This issue is fixed in version 4.0.4.
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Analysis
by VulDB Data Team • 10/28/2026
The i18next-http-backend library serves as a critical component for internationalization applications, facilitating the loading of translation resources across Node.js, browser-based environments, and Deno runtimes. A significant security flaw was identified within versions prior to 4.0.4 concerning the interpolateUrl function, which is responsible for constructing URLs by inserting dynamic values such as language codes and namespace identifiers into predefined loadPath or addPath templates. The core technical deficiency lies in the failure of this interpolation process to properly encode query string separators, specifically ampersands, equals signs, and semicolons. When an application template places variables like lng (language) or ns (namespace) directly into a query parameter position without adequate sanitization, these special characters are treated as literal data rather than structural delimiters for the URL structure itself.
This lack of input validation allows an attacker who controls the language or namespace values to inject additional parameters into the HTTP request sent by the backend layer. By appending sequences such as &key=value or ;param=data, the malicious actor can effectively override existing query parameters or introduce entirely new ones that are processed by the server-side translation service. This behavior constitutes a form of parameter pollution where the attacker manipulates the context in which subsequent requests operate. The vulnerability is particularly dangerous because it exploits the trust placed in user-supplied input within internationalization workflows, assuming that language codes and namespace identifiers are benign strings rather than potential vectors for structural manipulation.
The operational impact of this flaw extends beyond simple data leakage to include significant risks regarding access control and service integrity. If an application uses namespaces or tenant-specific identifiers as part of the URL structure, an attacker could potentially bypass isolation mechanisms by injecting parameters that force the backend to load resources from a different namespace or tenant context. This can lead to unauthorized exposure of sensitive translation strings intended for other users or administrative sections. Furthermore, if the backend interprets injected parameters in unexpected ways, it may alter its behavior, leading to denial-of-service conditions through malformed requests or enabling further exploitation chains that leverage the application's network position and existing credentials.
This issue is recognized as an incomplete fix for CVE-2026-41691, indicating a recurrence of similar logic errors in how dynamic URL components are handled within the library. From a classification perspective, this vulnerability aligns with CWE-79, which covers Improper Neutralization of Input During Web Page Generation, specifically focusing on cross-site scripting and parameter injection aspects when input is not properly encoded before being placed into web data structures. In terms of tactical mapping, it relates to ATT&CK techniques involving resource hijacking or manipulation of application logic through injected parameters, allowing attackers to influence the execution path of server-side processes based on client-controlled inputs.
To mitigate this vulnerability, organizations must immediately upgrade i18next-http-backend to version 4.0.4 or later, where the interpolation function has been patched to correctly encode special characters within query string values. For applications unable to update immediately due to dependency constraints, a temporary workaround involves implementing custom URL encoding logic for any language or namespace variables before they are passed into i18next configuration objects. Developers should ensure that all dynamic parts of URLs undergo strict validation and percent-encoding to prevent the injection of structural delimiters. Additionally, security teams should audit existing implementations to identify instances where user-controlled data influences backend request paths, ensuring that input sanitization is applied consistently across all internationalization endpoints to maintain the integrity of multi-tenant isolation and resource access controls.