gettext-converter: Prototype pollution in js2i18next() via crafted translation keys

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.9 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-55451: 0.57% estimated exploitation activity in the next 30 days; percentile 47.01 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact js2i18next() is vulnerable to prototype pollution. When converting translations, it splits nested keys on the key separator (default ##) and uses each segment as a dynamic object key while building the output object. A key whose segment is proto (e.g. proto##gcPolluted) causes the converter to resolve Object.prototype as the nested write target and assign the translated value onto it, polluting Object.prototype for the whole runtime. Any application that converts translation data (PO / i18next JS objects) originating from an untrusted or user-controlled source is affected. Prototype pollution can lead to denial of service and, depending on the surrounding application, may enable further attacks. Patches Fixed in gettext-converter@1.3.3. Key segments equal to proto, constructor, or prototype are now rejected before being used as dynamic object keys. Workarounds Upgrade to 1.3.3. If upgrading is not immediately possible, sanitize/validate translation keys before passing them to…

Published by the source

20 Aug 2026, 20:11 UTC

Last modified by the source

20 Aug 2026, 20:11 UTC

Source last checked

26 Oct 2026, 13:01 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-f4jp-rw7w-ccwg

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# Patch Next advisory brief: CVE-2026-55451

Advisory: gettext-converter: Prototype pollution in js2i18next() via crafted translation keys
IDs: CVE-2026-55451, GHSA-f4jp-rw7w-ccwg
Record: https://patchnext.com/advisories/cve-2026-55451 (revision 1, source checked 26 Oct 2026, 13:01 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: gettext-converter 1.3.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm gettext-converter: affected < 1.3.3; fixed in 1.3.3

## Suggested inspection (read-only)
- `npm ls gettext-converter --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on gettext-converter.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-f4jp-rw7w-ccwg (GitHub-reviewed advisory GHSA-f4jp-rw7w-ccwg lists affected ranges: npm gettext-converter >=0 <1.3.3)

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