GHSA-FV2F-RW9F-V9CM
Vulnerability from github – Published: 2026-05-15 15:30 – Updated: 2026-06-29 22:57smtp-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.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "smtp-server"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "3.18.3"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-38728"
],
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"github_reviewed": true,
"github_reviewed_at": "2026-06-29T22:57:15Z",
"nvd_published_at": "2026-05-15T15:16:51Z",
"severity": "HIGH"
},
"details": "smtp-server prior to v3.18.3 are vulnerable to unauthenticated memory exhaustion denial-of-service. smtp-server\u0027s command parser allows any remote client to consume server memory by sending data without newline characters. The server\u0027s `_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.\n\nThe `_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.",
"id": "GHSA-fv2f-rw9f-v9cm",
"modified": "2026-06-29T22:57:15Z",
"published": "2026-05-15T15:30:45Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-38728"
},
{
"type": "WEB",
"url": "https://github.com/nodemailer/smtp-server/commit/592c5666fa0c76d1d04c1a32abad0ef806fbfe97"
},
{
"type": "WEB",
"url": "https://bytecreator.dev/blog/CVE-2026-38728"
},
{
"type": "PACKAGE",
"url": "https://github.com/nodemailer/smtp-server"
},
{
"type": "WEB",
"url": "https://github.com/nodemailer/smtp-server/releases/tag/v3.18.3"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "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",
"type": "CVSS_V4"
}
],
"summary": "smtp-server\u0027s command parser memory exhaustion denial-of-service"
}
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