smtp-server's command parser memory exhaustion denial-of-service

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-38728: 0.57% estimated exploitation activity in the next 30 days; percentile 47.35 (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.

smtp-server prior to v3.18.3 are vulnerable to unauthenticated memory exhaustion denial-of-service. smtp-server's command parser allows any remote client to consume server memory by sending data without newline characters. The server's remainder buffer in SMTPStream.write grows without limit, leading to heap exhaustion, prolonged GC pauses that freeze the event loop, and in some cases, process crash. The write method in lib/smtp-stream.js appends incoming TCP chunks to this.remainder in command mode. The buffer is only emptied when a newline is found. If a client never sends a newline, the remainder value will grow indefinitely, causing excess memory consumption.

Published by the source

15 May 2026, 15:30 UTC

Last modified by the source

29 Jun 2026, 23:26 UTC

Source last checked

26 Oct 2026, 12:56 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-fv2f-rw9f-v9cm

2. Revision 2 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-fv2f-rw9f-v9cm

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# Patch Next advisory brief: CVE-2026-38728

Advisory: smtp-server's command parser memory exhaustion denial-of-service
IDs: CVE-2026-38728, GHSA-fv2f-rw9f-v9cm
Record: https://patchnext.com/advisories/cve-2026-38728 (revision 3, source checked 26 Oct 2026, 12:56 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: smtp-server 3.18.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm smtp-server: affected < 3.18.3; fixed in 3.18.3

## Suggested inspection (read-only)
- `npm ls smtp-server --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 smtp-server.
- 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-fv2f-rw9f-v9cm (OSV record GHSA-fv2f-rw9f-v9cm lists affected ranges: npm smtp-server >=0 <3.18.3 (fixed))
- Verified: https://github.com/advisories/GHSA-fv2f-rw9f-v9cm (GitHub-reviewed advisory GHSA-fv2f-rw9f-v9cm lists affected ranges: npm smtp-server >=0 <3.18.3)

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