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Medium

Security advisory

Type: advisorySources: OSVCVE: CVE-2017-15042

An unintended cleartext issue exists in Go before 1.8.4 and 1.9.x before 1.9.1. RFC 4954 requires that, during SMTP, the PLAIN auth scheme must only be used on network connections secured with TLS. The original implementation of smtp.PlainAuth in Go 1.0 enforced this requirement, and it was documented to do so. In 2013, upstream issue #5184, this was changed so that the server may decide whether PLAIN is acceptable. The result is that if you set up a man-in-the-middle SMTP server that doesn't advertise STARTTLS and does advertise that PLAIN auth is OK, the smtp.PlainAuth implementation sends the username and password.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2017-15042
Confirmed fixed CVEs
Not specified
Updated in this feed
31 Oct 2026, 09:51 UTC · Revision 1

Source evidence

CVE-2017-15042

core-osv · Original source

Published 5 Oct 2017, 21:29 UTC

An unintended cleartext issue exists in Go before 1.8.4 and 1.9.x before 1.9.1. RFC 4954 requires that, during SMTP, the PLAIN auth scheme must only be used on network connections secured with TLS. The original implementation of smtp.PlainAuth in Go 1.0 enforced this requirement, and it was documented to do so. In 2013, upstream issue #5184, this was changed so that the server may decide whether PLAIN is acceptable. The result is that if you set up a man-in-the-middle SMTP server that doesn't advertise STARTTLS and does advertise that PLAIN auth is OK, the smtp.PlainAuth implementation sends the username and password.

osv:CVE-2017-15042
Complete source record
{
  "id": "23b57280b7756d755833dc59bb69f79e7cf2788777ac86146408caf6a9825674",
  "url": "https://osv.dev/vulnerability/CVE-2017-15042",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "CVE-2017-15042",
    "summary": "An unintended cleartext issue exists in Go before 1.8.4 and 1.9.x before 1.9.1. RFC 4954 requires that, during SMTP, the PLAIN auth scheme must only be used on network connections secured with TLS. The original implementation of smtp.PlainAuth in Go 1.0 enforced this requirement, and it was documented to do so. In 2013, upstream issue #5184, this was changed so that the server may decide whether PLAIN is acceptable. The result is that if you set up a man-in-the-middle SMTP server that doesn't advertise STARTTLS and does advertise that PLAIN auth is OK, the smtp.PlainAuth implementation sends the username and password.",
    "evidence": "osv:CVE-2017-15042",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2017-15042",
      "aliases": [
        "CVE-2017-15042",
        "GO-2021-0178"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N"
        }
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                {
                  "introduced": "c8aec4095e089ff6ac50d18e97c3f46561f14f48"
                },
                {
                  "last_affected": "c8aec4095e089ff6ac50d18e97c3f46561f14f48"
                }
              ],
              "database_specific": {
                "extracted_events": [
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                    "cpe": "cpe:2.3:a:golang:go:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
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                        "last_affected": "1.8.3"
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                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:golang:go:1.9:*:*:*:*:*:*:*",
                    "range": [
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                        "introduced": "1.9"
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                    "source": "CPE_STRING"
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      "modified": "2026-10-20T10:48:13.467171660Z",
      "provider": "osv",
      "references": [
        "https://access.redhat.com/errata/RHSA-2017:3463",
        "https://access.redhat.com/errata/RHSA-2018:0878",
        "https://golang.org/cl/68210",
        "https://groups.google.com/d/msg/golang-dev/RinSE3EiJBI/kYL7zb07AgAJ",
        "https://security.gentoo.org/glsa/201710-23",
        "https://github.com/golang/go/issues/22134",
        "https://golang.org/cl/68023"
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      "provider_metadata": {}
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    "related_cves": [
      {
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        "evidence": "/id"
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    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 380157,
  "published_at": "2017-10-05T21:29:00.473+00:00"
}