CVE-2026-41885 is a medium-severity (CVSS 6.5) Path Traversal vulnerability in i18next-locize-backend. A fix is available for i18next-locize-backend — see the affected versions and patch details below.
Path traversal / URL injection via unsanitised lng/ns/projectId/version in i18next-locize-backend
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-41885.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-41885 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
i18next-locize-backendnpmDescription
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'againsthttps://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 replacesfor...initeration withObject.keys()plus an explicit prototype-key guard so a pollutedObject.prototypecannot leak into the merged options object. - New
utils.interpolateUrl/isSafeUrlSegment/sanitizeLogValue/redactUrlCredentialshelpers mirror the pattern shipped in[email protected](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
- CWE-22: Path Traversal
- CWE-74: Injection
- CWE-1321: Prototype Pollution (amplification path)
- Related advisory in the same ecosystem: GHSA-q89c-q3h5-w34g (i18next-http-backend)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | i18next-locize-backend | all versions | 9.0.2npm install i18next-locize-backend@9.0.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for i18next-locize-backend, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update i18next-locize-backend to 9.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-41885 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-41885 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-41885. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-41885 in your dependencies?
O3 Security finds CVE-2026-41885 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.