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VulnerabilityPublished

CVE-2026-63402: i18next · Modification of Assumed-Immutable Data (MAID)

Affects i18nextSource CVE Database V5

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Not known to be exploited · CVSS 5.9 Medium : upgrade to 26.3.4 when convenient.

Data as of 30 Oct 2026, 23:06 UTC

CVSS 3.1 base score
5.9Medium
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (GitHub_M)CVSS 3.15.9
Patch
Available – fixed in 26.3.4
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 30 Oct 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 to 26.3.4.

Affected software

ProductAffectedFixed in
i18nexti18nextAffected
  • <26.3.4
Fixed in
  • 26.3.4
npmi18nextpkg:npm/i18nextOther threatsAffected
  • <26.3.4
Fixed in
  • 26.3.4

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

AI-suggested

Upgrade i18next to version 26.3.4 or later, where this vulnerability is fixed. Applications not using `addResourceBundle` with both `deep: true` and `overwrite: true` are not vulnerable. No additional mitigation is required if the vulnerable configuration is not used. Since this is a library, ensure that all dependencies using i18next are also updated accordingly.

Description

CVE-2026-63402 is a vulnerability in the i18next JavaScript internationalization framework prior to version 26.3.4. It involves the `deepExtend` function improperly recursing into inherited built-in objects via the `in` operator, allowing an attacker to overwrite properties of shared built-in functions process-wide when specific parameters are used. This can cause unrecoverable denial of service by making functions like `hasOwnProperty` non-callable. The issue is fixed in version 26.3.4.

References

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