Summary
Versions of i18next-locize-backend prior to 9.0.2 interpolate lng, ns, projectId, and version directly into the configured loadPath / privatePath / addPath / updatePath / getLanguagesPath URL templates with no path-component validation and no encoding. When an application exposes any of these values to user-controlled input (?lng= / ?ns= query parameters via i18next-browser-languagedetector, cookies, request headers, or a URL-derived projectId), a crafted value can change the structure of the outgoing request URL.
Affected call sites in lib/index.js (pre-patch): the interpolate() helper is used at the five URL-build sites — _readAny/read (line 415 for private, 426 for public), getLanguages (lines 271 and 296), and writePage (lines 616 and 622) for the missing-key and update POST paths. The helper interpolate in lib/utils.js substitutes raw values with no encoding.
Impact
An attacker who can influence lng, ns, projectId, or version can:
- Path traversal —
lng = '../../admin' against https://api.locize.app/{{projectId}}/{{version}}/{{lng}}/{{ns}} changes the request URL path segment that reaches the locize CDN / API.
- Query-string injection —
lng = 'en?x=y' appends an attacker-chosen query to the URL.
- Fragment truncation —
lng = 'en#x' silently truncates the path in browser fetches.
- URL-encoded bypass —
lng = 'en%2F..' leverages server-side decoding to reintroduce /...
The worst-case concrete impact is loading an unintended translation resource (potentially causing wrong content to render) and, when a custom loadPath is configured against an internal / file-scheme URL, SSRF or arbitrary-file read on the host running the backend.
Additionally, the pre-patch interpolate() function read data[key] without excluding prototype-chain properties — under prototype-pollution conditions in the same process, that path could pull values from Object.prototype into the URL.
Related fixes shipped in 9.0.2
- The
defaults() helper replaces for...in iteration with Object.keys() plus an explicit prototype-key guard so a polluted Object.prototype cannot leak into the merged options object.
- New
utils.interpolateUrl / isSafeUrlSegment / sanitizeLogValue / redactUrlCredentials helpers mirror the pattern shipped in i18next-http-backend@3.0.5 (see its advisory GHSA-q89c-q3h5-w34g).
Affected versions
All versions of i18next-locize-backend prior to 9.0.2.
Patch
Fixed in 9.0.2. lib/index.js now uses interpolateUrl() at every URL-build site and returns an error callback (or silently drops the queued write for writePage) when any interpolated value fails the safety check. Legitimate i18next language-code shapes (BCP-47, en_US, zh-Hant-HK, my-custom.ns, +-joined multi-language values) all pass.
Workarounds
No workaround short of upgrading. If you cannot upgrade immediately, sanitise lng / ns / projectId / version at your application boundary before passing them through to i18next — reject values containing .., /, \, ?, #, %, whitespace, control characters, and cap the length.
Credits
Discovered via an internal security audit of the i18next / locize ecosystem.
References
References
Summary
Versions of
i18next-locize-backendprior to 9.0.2 interpolatelng,ns,projectId, andversiondirectly into the configuredloadPath/privatePath/addPath/updatePath/getLanguagesPathURL templates with no path-component validation and no encoding. When an application exposes any of these values to user-controlled input (?lng=/?ns=query parameters viai18next-browser-languagedetector, cookies, request headers, or a URL-derivedprojectId), a crafted value can change the structure of the outgoing request URL.Affected call sites in
lib/index.js(pre-patch): theinterpolate()helper is used at the five URL-build sites —_readAny/read(line 415 for private, 426 for public),getLanguages(lines 271 and 296), andwritePage(lines 616 and 622) for the missing-key and update POST paths. The helperinterpolateinlib/utils.jssubstitutes raw values with no encoding.Impact
An attacker who can influence
lng,ns,projectId, orversioncan:lng = '../../admin'againsthttps://api.locize.app/{{projectId}}/{{version}}/{{lng}}/{{ns}}changes the request URL path segment that reaches the locize CDN / API.lng = 'en?x=y'appends an attacker-chosen query to the URL.lng = 'en#x'silently truncates the path in browser fetches.lng = 'en%2F..'leverages server-side decoding to reintroduce/...The worst-case concrete impact is loading an unintended translation resource (potentially causing wrong content to render) and, when a custom
loadPathis configured against an internal / file-scheme URL, SSRF or arbitrary-file read on the host running the backend.Additionally, the pre-patch
interpolate()function readdata[key]without excluding prototype-chain properties — under prototype-pollution conditions in the same process, that path could pull values fromObject.prototypeinto the URL.Related fixes shipped in 9.0.2
defaults()helper replacesfor...initeration withObject.keys()plus an explicit prototype-key guard so a pollutedObject.prototypecannot leak into the merged options object.utils.interpolateUrl/isSafeUrlSegment/sanitizeLogValue/redactUrlCredentialshelpers mirror the pattern shipped ini18next-http-backend@3.0.5(see its advisory GHSA-q89c-q3h5-w34g).Affected versions
All versions of
i18next-locize-backendprior to 9.0.2.Patch
Fixed in 9.0.2.
lib/index.jsnow usesinterpolateUrl()at every URL-build site and returns an error callback (or silently drops the queued write forwritePage) when any interpolated value fails the safety check. Legitimate i18next language-code shapes (BCP-47,en_US,zh-Hant-HK,my-custom.ns,+-joined multi-language values) all pass.Workarounds
No workaround short of upgrading. If you cannot upgrade immediately, sanitise
lng/ns/projectId/versionat your application boundary before passing them through to i18next — reject values containing..,/,\,?,#,%, whitespace, control characters, and cap the length.Credits
Discovered via an internal security audit of the i18next / locize ecosystem.
References
References