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VulnerabilityPublished

CVE-2026-48714: i18next-http-middleware · Prototype Pollution

Affects i18next-http-middlewareSource CVE Database V5

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Not known to be exploited · CVSS 9.1 Critical : upgrade to 3.9.7 as a priority.

Data as of 31 Oct 2026, 08:20 UTC

CVSS 3.1 base score
9.1Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.5% chance of exploitation in 30 days – higher than 43% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 3.9.7
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 15 Jun 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade i18next-http-middleware to 3.9.7.

Affected software

ProductAffectedFixed in
i18nexti18next-http-middlewareAffected
  • <3.9.7
Fixed in
  • 3.9.7
npmi18next-http-middlewarepkg:npm/i18next-http-middlewareOther threatsAffected
  • <3.9.7
Fixed in
  • 3.9.7

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fixed version 3.9.7 of i18next-http-middleware is available and should be applied to remediate this vulnerability. If immediate upgrade is not possible, developers should ensure missingKeyHandler is not exposed to untrusted users by mounting it behind authentication or removing the route. Additionally, implement a request-body filter that rejects any top-level keys containing __proto__, constructor, or prototype after splitting on the configured keySeparator. Also, disable missing-key persistence by setting saveMissing to false when accepting writes from untrusted input. These mitigations reduce exposure until the official fix can be applied.

Description

A prototype pollution vulnerability exists in i18next-http-middleware versions prior to 3.9.7. The middleware's missingKeyHandler blocks literal keys like __proto__, constructor, and prototype but does not block dotted variants such as "__proto__.polluted". When used with downstream backends like i18next-fs-backend ≤ 2.6.5 that split keys on a configured separator and write to Object.prototype without proper guards, this can lead to remote prototype pollution. This may cause crashes, corrupted translation behavior, configuration poisoning, or bypasses of property-based security checks. The issue is fixed in version 3.9.7.

References

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