Lettermint Node.js SDK leaks email properties to unintended recipients when client instance is reused

Exploitation

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

CVSS

4.7 · CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-27492: 0.19% estimated exploitation activity in the next 30 days; percentile 8.31 (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 Email properties (such as to, subject, html, text, and attachments) are not reset between sends when a single client instance is reused across multiple .send() calls. This can cause properties from a previous send to leak into a subsequent one, potentially delivering content or recipient addresses to unintended parties. Applications sending emails to different recipients in sequence — such as transactional flows like password resets or notifications — are affected. Patches Yes, the issue has been patched. Users should upgrade to v1.5.1 or later. Workarounds If upgrading immediately is not possible, instantiate a new client for each send: This ensures no state is carried over between sends.

Published by the source

20 Feb 2026, 21:14 UTC

Last modified by the source

23 Feb 2026, 22:53 UTC

Source last checked

26 Oct 2026, 12:42 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-49pc-8936-wvfp

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-49pc-8936-wvfp

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# Patch Next advisory brief: CVE-2026-27492

Advisory: Lettermint Node.js SDK leaks email properties to unintended recipients when client instance is reused
IDs: CVE-2026-27492, GHSA-49pc-8936-wvfp
Record: https://patchnext.com/advisories/cve-2026-27492 (revision 2, source checked 26 Oct 2026, 12:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: lettermint 1.5.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm lettermint: affected < 1.5.1; fixed in 1.5.1

## Suggested inspection (read-only)
- `npm ls lettermint --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 lettermint.
- 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://osv.dev/vulnerability/GHSA-49pc-8936-wvfp (OSV record GHSA-49pc-8936-wvfp lists affected ranges: npm lettermint >=0 <1.5.1 (fixed))
- Verified: https://github.com/advisories/GHSA-49pc-8936-wvfp (GitHub-reviewed advisory GHSA-49pc-8936-wvfp lists affected ranges: npm lettermint >=0 <1.5.1)

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