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Security advisory

Type: advisorySources: OSVCVE: CVE-2023-51766

Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations. Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because Exim supports . but some other popular e-mail servers do not.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2023-51766
Confirmed fixed CVEs
Not specified
Updated in this feed
2 Nov 2026, 21:18 UTC · Revision 1

Source evidence

CVE-2023-51766

core-osv · Original source

Published 24 Dec 2023, 00:00 UTC

Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations. Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because Exim supports . but some other popular e-mail servers do not.

osv:CVE-2023-51766
Complete source record
{
  "id": "5fe604de6eb644760e070333a3ecb5ace65ac6aac18869bb68c80d865e2eda7f",
  "url": "https://osv.dev/vulnerability/CVE-2023-51766",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "CVE-2023-51766",
    "summary": "Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations. Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because Exim supports . but some other popular e-mail servers do not.",
    "evidence": "osv:CVE-2023-51766",
    "products": [],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2023-51766",
      "aliases": [
        "CVE-2023-51766"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/exim/exim",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "5a8fc079931410b30889e69f890857b05ca8d4b2"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:exim:exim:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "4.97.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "exim-4.97",
            "exim-4.97-RC2",
            "exim-4.96",
            "exim-4.97-RC1",
            "exim-4.97-RC0",
            "exim-4.95",
            "exim-4.96-RC2",
            "exim-4.96-RC1",
            "exim-4.96-RC0",
            "exim-4.95-RC2",
            "exim-4.95-RC1",
            "exim-4.95-RC0",
            "exim-4.94",
            "exim-4.94-RC2",
            "exim-4.94-RC1",
            "exim-4_94_RC0",
            "exim-4.93",
            "exim-4.93-RC7",
            "exim-4.93-RC6",
            "exim-4.93-RC5",
            "exim-4.93-RC4",
            "exim-4.93-RC3",
            "exim-4.93-RC2",
            "exim-4.93-RC1",
            "exim-4.93-RC0",
            "exim-4.92-jgh",
            "exim-4.92-RC6",
            "exim-4.92",
            "exim-4.92-RC5",
            "exim-4.92-RC4",
            "exim-4.92-RC3",
            "exim-4.92-RC2",
            "exim-4.92-RC1",
            "exim-4_91",
            "exim-4_91_RC4",
            "exim-4_91_RC3",
            "exim-4_91_RC2",
            "exim-4_91_RC1",
            "exim-4_90_RC4",
            "exim-4_90",
            "exim-4_90_RC3",
            "exim-4_90_RC2",
            "exim-4_90_RC1",
            "exim-4.90devstart",
            "exim-4_89_RC3",
            "exim-4_89_RC1",
            "exim-4_88",
            "exim-4_87",
            "exim-4_88_RC6",
            "exim-4_88_RC5",
            "exim-4_88_RC4",
            "exim-4_88_RC3",
            "exim-4_88_RC2",
            "exim-4_88_RC1",
            "exim-4_87_RC7",
            "exim-4_87_RC6",
            "exim-4_87_RC5",
            "exim-4_87_RC4",
            "exim-4_84",
            "exim-4_86",
            "exim-4_85",
            "exim-4_87_RC3",
            "exim-4_87_RC2",
            "exim-4_87_RC1",
            "exim-4_86_RC5",
            "exim-4_86_RC4",
            "exim-4_86_RC3",
            "exim-4_86_RC2",
            "exim-4_86_RC1",
            "exim-4_85_RC4",
            "exim-4_85_RC3",
            "exim-4_85_RC2",
            "exim-4_85_RC1",
            "exim-4_84_RC2",
            "exim-4_84_RC1",
            "exim-4_83",
            "exim-4_83_RC3",
            "exim-4_83_RC2",
            "exim-4_83_RC1",
            "exim-4_82",
            "exim-4_82_RC5",
            "exim-4_82_RC4",
            "exim-4_82_RC3",
            "exim-4_82_RC2",
            "exim-4_82_RC1",
            "exim-4_80",
            "exim-4_80_RC7",
            "exim-4_80_RC6",
            "exim-4_80_RC5",
            "exim-4_80_RC4",
            "exim-4_80_RC3",
            "exim-4_80_RC2",
            "exim-4_80_RC1",
            "exim-4_77",
            "exim-4_77_RC4",
            "exim-4_77_RC3",
            "exim-4_77_RC2",
            "exim-4_77_RC1",
            "exim-4_76",
            "exim-4_76_RC2",
            "exim-4_76_RC1",
            "exim-4_75",
            "exim-4_75_RC3",
            "exim-4_75_RC2",
            "exim-4_75_RC1",
            "exim-4_74",
            "exim-4_74_RC1",
            "exim-4_73",
            "exim-4_73_RC1",
            "exim-4_73_RC00",
            "exim-4_72",
            "exim-4_72_RC2",
            "exim-4_72_RC1",
            "exim-4_71",
            "exim-4_70",
            "exim-4_70_RC4",
            "exim-4_70_RC3",
            "DEVEL_PDKIM_START",
            "exim-4_69",
            "exim-4_68",
            "exim-4_67",
            "exim-4_66",
            "exim-4_65",
            "exim-4_64",
            "exim-4_63",
            "exim-4_62",
            "exim-4_61",
            "exim-4_54",
            "exim-4_53",
            "exim-4_52",
            "exim-4_51",
            "exim-4_50"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2023-51766.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:23.560818935Z",
      "provider": "osv",
      "references": [
        "https://bugs.exim.org/show_bug.cgi?id=3063",
        "https://exim.org/static/doc/security/CVE-2023-51766.txt",
        "https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html",
        "https://git.exim.org/exim.git/commit/5bb786d5ad568a88d50d15452aacc8404047e5ca",
        "https://git.exim.org/exim.git/commit/cf1376206284f2a4f11e32d931d4aade34c206c5",
        "https://github.com/Exim/exim/blob/master/doc/doc-txt/cve-2023-51766",
        "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/",
        "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/",
        "https://lwn.net/Articles/956533/",
        "https://www.openwall.com/lists/oss-security/2023/12/23/2",
        "https://www.youtube.com/watch?v=V8KPV96g1To",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/51xxx/CVE-2023-51766.json",
        "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/",
        "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/",
        "https://nvd.nist.gov/vuln/detail/CVE-2023-51766",
        "https://bugzilla.redhat.com/show_bug.cgi?id=2255852",
        "https://lists.debian.org/debian-lts-announce/2024/01/msg00002.html",
        "https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/"
      ],
      "provider_metadata": {
        "cna_assigner": "mitre",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/51xxx/CVE-2023-51766.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2023-51766",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 490184,
  "published_at": "2023-12-24T00:00:00+00:00"
}