How severe is CVE-2026-48713?

CVE-2026-48713 has a CVSS score of 9.1/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-48713?

CVE-2026-48713 affects the following packages: i18next-fs-backend (npm). Ecosystems affected: npm.

How do I fix CVE-2026-48713?

Update i18next-fs-backend to 2.6.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48713 is resolved across your whole dependency graph.

How do I detect CVE-2026-48713 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for i18next-fs-backend, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-48713 if there is no patch (or I can't update yet)?

Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Is CVE-2026-48713 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-48713 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-48713?

CVE-2026-48713 has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 49th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-48713?

CVE-2026-48713 is classified as CWE-1321 (CWE-1321). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-48713 published, and has it been updated?

CVE-2026-48713 was published on June 15, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

CRITICAL severity

CVE-2026-48713 — i18next-fs-backend

CRITICALFix: i18next/i18next-fs-backend@3ab0448

CVE-2026-48713 is a critical-severity (CVSS 9.1) CWE-1321 vulnerability in i18next-fs-backend. A fix is available for i18next-fs-backend — see the affected versions and patch details below.

i18next-fs-backend: Prototype pollution via crafted missing-key string

Also known asGHSA-2933-q333-qg83

Published

Jun 15, 2026

Updated

Aug 12, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 27, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
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-2026-48713.

EPSS Exploitation Probability

via FIRST.org ↗

0.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs49th percentile — riskier than 49% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-48713 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 379,842 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

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.

243other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

i18next-fs-backendnpm

1.4Mdownloads / week

Description

Impact

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.

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.

Affected configuration

Applications are directly affected only if all of the following hold:

i18next-fs-backend ≤ 2.6.5 is configured as the backend.
i18next-http-middleware's missingKeyHandler (or another route that forwards untrusted request bodies to i18next.t(..., { ... }) with saveMissing: true) is reachable by untrusted users.
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.

Patches

Fixed 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.

A matching defence-in-depth fix has been shipped in i18next-http-middleware 3.9.7 — see the companion advisory.

Workarounds

If users cannot upgrade immediately:

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.
Set keySeparator: false in the i18next options to disable backend key splitting (note: this also disables nested translation keys).

Resources

Original report by @codeswhite.
Companion advisory in i18next-http-middleware: GHSA-f49m-vf83-692w.
Previous i18next-fs-backend security release: GHSA-8847-338w-5hcj (path traversal via lng/ns, fixed in 2.6.4).

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`i18next-fs-backend`	all versions	2.6.6`npm install i18next-fs-backend@2.6.6`

Affected Products

1 product · 1 configurations

Application

i18next-fs-backendi18next

< 2.6.6

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for i18next-fs-backend, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update i18next-fs-backend to 2.6.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48713 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Frequently Asked Questions

### Impact `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. `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.