{"id":"EUVD-2026-37005","revision":null,"records":[{"revision":"aeea44a1c51640ea9a2a93fabc23bd43","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-48713","aliases":[],"title":"i18next-fs-backend: Prototype pollution via crafted missing-key string","description":"Versions prior to 2.6.6 are vulnerable to prototype pollution via crafted missing-key strings when used to persist missing translation keys (e.g. via i18next-http-middleware's missingKeyHandler exposed to untrusted input). Backend.writeFile() splits each queued missing-key string on the configured keySeparator (default .) before calling the internal setPath() walker. The walker (getLastOfPath in lib/utils.js) did not guard against unsafe segments, so a key like \"__proto__.polluted\" was split into [\"__proto__\", \"polluted\"] and walked straight into Object.prototype, allowing an attacker to write arbitrary properties onto the global object prototype. Depending on the host application, polluted prototype properties may cause crashes, corrupted translation behaviour, configuration poisoning, or bypasses of property-based security checks. Applications are affected only if the missingKeyHandler (or another route that forwards untrusted request bodies to i18next.t(..., { ... }) with saveMissing: true) is reachable by untrusted users and the default behaviour of splitting missing-key strings on keySeparator is in use (i.e. keySeparator is not false). Apps that do not expose missing-key persistence to untrusted input are not directly affected through this attack path. This issue has been fixed in version 2.6.6. If developers using the library are unable to upgrade immediately, they should take the following precautions: do not expose i18next-http-middleware's missingKeyHandler to untrusted users (mount it behind authentication, or remove the route), disable missing-key persistence (saveMissing: false, or no backend.create implementation) when accepting writes from untrusted input, and set keySeparator: false in their i18next options to disable backend key splitting (note: this also disables nested translation keys).","state":0,"publishedAt":"2026-06-15T20:31:53.929+00:00","modifiedAt":"2026-06-16T12:49:24.673+00:00","affected":[{"ecosystem":"Vendor product","name":"i18next-fs-backend","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"i18next\",\n                    \"product\": \"i18next-fs-backend\",\n                    \"versions\": [\n                        {\n                            \"version\": \"< 2.6.6\",\n                            \"status\": \"affected\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H","score":9.1,"severity":"CRITICAL"}],"references":["https://github.com/i18next/i18next-fs-backend/security/advisories/GHSA-2933-q333-qg83","https://github.com/i18next/i18next-fs-backend/commit/3ab0448087da6935a40117f904b7457281f963f4"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-48713","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-48713","identifiers":["CVE-2026-48713"]},"retained":false,"historicalAffected":[]},{"revision":"439485dc3cd346e896bf858ca997e654","observedAt":"2026-11-07T11:30:20.214+00:00","statement":{"source":"euvd","id":"EUVD-2026-37005","aliases":["CVE-2026-48713","GHSA-2933-q333-qg83"],"title":"Versions prior to 2.6.6 are vulnerable to prototype pollution via crafted missing-key strings when used to persist missing translation keys (e.g. via i18next-http-middleware's missingKeyHandler exposed to untrusted input). Backend.writeFile…","description":"Versions prior to 2.6.6 are vulnerable to prototype pollution via crafted missing-key strings when used to persist missing translation keys (e.g. via i18next-http-middleware's missingKeyHandler exposed to untrusted input). Backend.writeFile() splits each queued missing-key string on the configured keySeparator (default .) before calling the internal setPath() walker. The walker (getLastOfPath in lib/utils.js) did not guard against unsafe segments, so a key like \"__proto__.polluted\" was split into [\"__proto__\", \"polluted\"] and walked straight into Object.prototype, allowing an attacker to write arbitrary properties onto the global object prototype. Depending on the host application, polluted prototype properties may cause crashes, corrupted translation behaviour, configuration poisoning, or bypasses of property-based security checks. Applications are affected only if the missingKeyHandler (or another route that forwards untrusted request bodies to i18next.t(..., { ... }) with saveMissing: true) is reachable by untrusted users and the default behaviour of splitting missing-key strings on keySeparator is in use (i.e. keySeparator is not false). Apps that do not expose missing-key persistence to untrusted input are not directly affected through this attack path. This issue has been fixed in version 2.6.6. If developers using the library are unable to upgrade immediately, they should take the following precautions: do not expose i18next-http-middleware's missingKeyHandler to untrusted users (mount it behind authentication, or remove the route), disable missing-key persistence (saveMissing: false, or no backend.create implementation) when accepting writes from untrusted input, and set keySeparator: false in their i18next options to disable backend key splitting (note: this also disables nested translation keys).","state":0,"publishedAt":null,"modifiedAt":null,"affected":[],"metrics":[{"system":"EUVD CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H","score":9.1,"severity":null}],"references":["https://github.com/i18next/i18next-fs-backend/security/advisories/GHSA-2933-q333-qg83","https://github.com/i18next/i18next-fs-backend/commit/3ab0448087da6935a40117f904b7457281f963f4"],"sourceUrl":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-37005","license":"ENISA EUVD · source terms and attribution apply","enrichment":{"sourceStatus":null,"weaknesses":[],"productCriteria":[],"sourceDates":{"datePublished":"Jun 15, 2026, 8:31:53 PM","dateUpdated":"Jun 16, 2026, 12:49:24 PM"},"relatedAdvisories":[],"note":"EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON."},"key":"euvd:EUVD-2026-37005","identifiers":["EUVD-2026-37005","CVE-2026-48713","GHSA-2933-q333-qg83"]},"retained":false,"historicalAffected":[]},{"revision":"d68fd9ca9f2a466ca1393fcbcbd3d11a","observedAt":"2026-10-27T13:11:53.172+00:00","statement":{"source":"nvd","id":"CVE-2026-48713","aliases":[],"title":"Versions prior to 2.6.6 are vulnerable to prototype pollution via crafted missing-key strings when used to persist missing translation keys (e.g. via i18next-http-middleware's missingKeyHandler exposed to untrusted input). Backend.writeFile…","description":"Versions prior to 2.6.6 are vulnerable to prototype pollution via crafted missing-key strings when used to persist missing translation keys (e.g. via i18next-http-middleware's missingKeyHandler exposed to untrusted input). Backend.writeFile() splits each queued missing-key string on the configured keySeparator (default .) before calling the internal setPath() walker. The walker (getLastOfPath in lib/utils.js) did not guard against unsafe segments, so a key like \"__proto__.polluted\" was split into [\"__proto__\", \"polluted\"] and walked straight into Object.prototype, allowing an attacker to write arbitrary properties onto the global object prototype. Depending on the host application, polluted prototype properties may cause crashes, corrupted translation behaviour, configuration poisoning, or bypasses of property-based security checks. Applications are affected only if the missingKeyHandler (or another route that forwards untrusted request bodies to i18next.t(..., { ... }) with saveMissing: true) is reachable by untrusted users and the default behaviour of splitting missing-key strings on keySeparator is in use (i.e. keySeparator is not false). Apps that do not expose missing-key persistence to untrusted input are not directly affected through this attack path. This issue has been fixed in version 2.6.6. If developers using the library are unable to upgrade immediately, they should take the following precautions: do not expose i18next-http-middleware's missingKeyHandler to untrusted users (mount it behind authentication, or remove the route), disable missing-key persistence (saveMissing: false, or no backend.create implementation) when accepting writes from untrusted input, and set keySeparator: false in their i18next options to disable backend key splitting (note: this also disables nested translation keys).","state":0,"publishedAt":"2026-06-15T22:16:17.397+00:00","modifiedAt":"2026-10-25T23:10:00.167+00:00","affected":[],"metrics":[{"system":"CVSS 3.1 · security-advisories@github.com · Secondary","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H","score":9.1,"severity":"CRITICAL"}],"references":["https://github.com/i18next/i18next-fs-backend/commit/3ab0448087da6935a40117f904b7457281f963f4","https://github.com/i18next/i18next-fs-backend/security/advisories/GHSA-2933-q333-qg83"],"sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-48713","license":"NIST NVD usage terms; underlying source attribution retained","enrichment":{"sourceStatus":"Analyzed","weaknesses":["CWE-1321"],"productCriteria":["cpe:2.3:a:i18next:i18next-fs-backend:*:*:*:*:*:node.js:*:*"],"sourceDates":{"published":"2026-06-15T22:16:17.397","lastModified":"2026-10-25T23:10:00.167"},"relatedAdvisories":[],"note":"NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2026-48713","identifiers":["CVE-2026-48713"]},"retained":false,"historicalAffected":[]},{"revision":"0203ed2cbd3347198dc793055c32b4c5","observedAt":"2026-10-24T13:17:17.793+00:00","statement":{"source":"osv","id":"GHSA-2933-q333-qg83","aliases":["CVE-2026-48713"],"title":"i18next-fs-backend vulnerable to prototype pollution via crafted missing-key string","description":"### Impact\n\n`i18next-fs-backend` ≤ 2.6.5, when used to persist missing translation keys (e.g. via `i18next-http-middleware`'s `missingKeyHandler` exposed to untrusted input), is vulnerable to prototype pollution via crafted missing-key strings.\n\n`Backend.writeFile()` splits each queued missing-key string on the configured `keySeparator` (default `.`) before calling the internal `setPath()` walker. The walker (`getLastOfPath` in `lib/utils.js`) did not guard against unsafe segments, so a key like `\"__proto__.polluted\"` was split into `[\"__proto__\", \"polluted\"]` and walked straight into `Object.prototype`, allowing an attacker to write arbitrary properties onto the global object prototype.\n\nDepending on the host application, polluted prototype properties may cause crashes, corrupted translation behaviour, configuration poisoning, or bypasses of property-based security checks.\n\n### Affected configuration\n\nApplications are directly affected only if **all** of the following hold:\n\n- `i18next-fs-backend` ≤ 2.6.5 is configured as the backend.\n- `i18next-http-middleware`'s `missingKeyHandler` (or another route that forwards untrusted request bodies to `i18next.t(..., { ... })` with `saveMissing: true`) is reachable by untrusted users.\n- The default behaviour of splitting missing-key strings on `keySeparator` is in use (i.e. `keySeparator` is not `false`).\n\nApps that do not expose missing-key persistence to untrusted input are not directly affected through this attack path.\n\n### Patches\n\nFixed in **i18next-fs-backend 2.6.6**. The traversal helper now refuses to descend through `__proto__`, `constructor`, or `prototype` segments and drops the offending write silently. Legitimate dotted keys (e.g. `\"header.title\"`) are unaffected.\n\nA matching defence-in-depth fix has been shipped in `i18next-http-middleware` **3.9.7** — see the companion advisory.\n\n### Workarounds\n\nIf users cannot upgrade immediately:\n\n- Do not expose `i18next-http-middleware`'s `missingKeyHandler` to untrusted users (mount it behind authentication, or remove the route).\n- Disable missing-key persistence (`saveMissing: false`, or no `backend.create` implementation) when accepting writes from untrusted input.\n- Set `keySeparator: false` in the i18next options to disable backend key splitting (note: this also disables nested translation keys).\n\n### Resources\n\n- Original report by [@codeswhite](https://github.com/codeswhite).\n- Companion advisory in `i18next-http-middleware`: [GHSA-f49m-vf83-692w](https://github.com/i18next/i18next-http-middleware/security/advisories/GHSA-f49m-vf83-692w).\n- Previous `i18next-fs-backend` security release: GHSA-8847-338w-5hcj (path traversal via `lng`/`ns`, fixed in 2.6.4).","state":0,"publishedAt":"2026-06-25T17:28:46+00:00","modifiedAt":"2026-06-25T17:56:29.668069+00:00","affected":[{"ecosystem":"npm","name":"i18next-fs-backend","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"2.6.6"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"CRITICAL"}],"references":["https://github.com/i18next/i18next-fs-backend/security/advisories/GHSA-2933-q333-qg83","https://nvd.nist.gov/vuln/detail/CVE-2026-48713","https://github.com/i18next/i18next-fs-backend/commit/3ab0448087da6935a40117f904b7457281f963f4","https://github.com/i18next/i18next-fs-backend"],"sourceUrl":"https://github.com/advisories/GHSA-2933-q333-qg83","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-2933-q333-qg83","identifiers":["GHSA-2933-q333-qg83","CVE-2026-48713"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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