Is CVE-2026-48713 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-48713 being exploited in the wild.

How severe is CVE-2026-48713?

Critical severity, with a CVSS score of 9.1, published 15 June 2026.

Which products and versions are affected?

i18next-fs-backend (npm) < 2.6.6, SEMVER:introduced=0,fixed=2.6.6.

Is there a fix for CVE-2026-48713?

Yes. i18next-fs-backend (npm): upgrade to 2.6.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-48713 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-48713?

Check whether you run i18next-fs-backend (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-48713: i18next-fs-backend prototype pollution in missing-key persistence

Q: Is there a fix for CVE-2026-48713?

Yes. i18next-fs-backend (npm): upgrade to 2.6.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-48713 attacked?

It is attacked over the network, in a software library.

Q: Am I affected by CVE-2026-48713?

Check whether you run i18next-fs-backend (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-48713 · Severity: critical · CVSS 9.1 · Published 2026-06-15

i18next-fs-backend is a Node.js library that handles translation file management for the i18next internationalization framework. When configured to save missing translation keys (especially via i18next-http-middleware), the library fails to sanitize user-supplied key names before storing them. An attacker can inject specially crafted key strings to pollute the JavaScript object prototype, causing application misbehavior, crashes, or bypassing security checks—similar to injecting code into a system's core configuration layer.

Vendors: npm.

Quick answers

Is CVE-2026-48713 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-48713 being exploited in the wild.
How severe is CVE-2026-48713?: Critical severity, with a CVSS score of 9.1, published 15 June 2026.
Which products and versions are affected?: i18next-fs-backend (npm) < 2.6.6, SEMVER:introduced=0,fixed=2.6.6.
Is there a fix for CVE-2026-48713?: Yes. i18next-fs-backend (npm): upgrade to 2.6.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-48713 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-48713?: Check whether you run i18next-fs-backend (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

i18next-fs-backend (npm): upgrade to 2.6.6 or later
```
npm install i18next-fs-backend@2.6.6
```

Technical details

The vulnerability is a prototype pollution flaw (CWE-1321) in the i18next-fs-backend library, versions ≤ 2.6.5. The Backend.writeFile() method splits missing-key strings on the configured keySeparator (default ".") before passing them to an internal setPath() traversal helper. The getLastOfPath() function in lib/utils.js fails to block traversal through dangerous prototype property names like "__proto__", "constructor", and "prototype". An attacker can reach this code by supplying crafted key names to endpoints like i18next-http-middleware's missingKeyHandler when saveMissing is enabled, if that handler is exposed to untrusted input. By submitting a key such as "__proto__.polluted", the attacker causes the walker to traverse into Object.prototype and set arbitrary global properties. The fix in version 2.6.6 guards the traversal helper to refuse descending through unsafe segments and silently drops offending writes. A defense-in-depth patch was also released in i18next-http-middleware 3.9.7.

Affected products

i18next i18next-fs-backend < 2.6.6

Identifiers

CVE-2026-48713
GHSA-2933-q333-qg83

Timeline

2026-05-22: advisory: Coordinated disclosure by @codeswhite
2026-05-22: patched: Fixed in i18next-fs-backend 2.6.6
2026-06-25: disclosed

References

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