{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-55558",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-20T20:00:16.093023Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-08-20T20:00:21.869Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "aiosmtplib",
          "vendor": "cole",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 5.1.2"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "aiosmtplib is an asynchronous SMTP client for use with asyncio. Prior to 5.1.2, SMTPProtocol.start_tls in src/aiosmtplib/protocol.py consumes the server\u0027s 220 response and starts the TLS handshake without clearing SMTPProtocol._buffer. An active network attacker can place attacker-chosen SMTP response lines after the plaintext 220 response in the same network segment. The method then calls loop.start_tls; those bytes survive the transport upgrade and are parsed as the first response from inside the TLS session, desynchronizing subsequent SMTP command and response pairs. Connections using start_tls=True or opportunistic STARTTLS are affected, while connections using use_tls=True are not. This issue is fixed in version 5.1.2."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 5.9,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-74",
              "description": "CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component (\u0027Injection\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-20T14:29:58.580Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/cole/aiosmtplib/security/advisories/GHSA-vxj7-4xrp-5vr4",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/cole/aiosmtplib/security/advisories/GHSA-vxj7-4xrp-5vr4"
        },
        {
          "name": "https://github.com/cole/aiosmtplib/commit/9fab7ba1361dbf7622ede1315a24be805cff09c9",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/cole/aiosmtplib/commit/9fab7ba1361dbf7622ede1315a24be805cff09c9"
        },
        {
          "name": "https://github.com/cole/aiosmtplib/releases/tag/v5.1.2",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/cole/aiosmtplib/releases/tag/v5.1.2"
        }
      ],
      "source": {
        "advisory": "GHSA-vxj7-4xrp-5vr4",
        "discovery": "UNKNOWN"
      },
      "title": "aiosmtplib: STARTTLS response injection"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-55558",
    "datePublished": "2026-08-20T14:29:58.580Z",
    "dateReserved": "2026-06-16T23:11:20.213Z",
    "dateUpdated": "2026-08-20T20:00:21.869Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-55558\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-08-20T20:00:16.093023Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-08-20T20:00:18.930Z\"}}], \"cna\": {\"title\": \"aiosmtplib: STARTTLS response injection\", \"source\": {\"advisory\": \"GHSA-vxj7-4xrp-5vr4\", \"discovery\": \"UNKNOWN\"}, \"metrics\": [{\"cvssV3_1\": {\"scope\": \"UNCHANGED\", \"version\": \"3.1\", \"baseScore\": 5.9, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"MEDIUM\", \"vectorString\": \"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N\", \"integrityImpact\": \"HIGH\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"HIGH\", \"availabilityImpact\": \"NONE\", \"privilegesRequired\": \"NONE\", \"confidentialityImpact\": \"NONE\"}}], \"affected\": [{\"vendor\": \"cole\", \"product\": \"aiosmtplib\", \"versions\": [{\"status\": \"affected\", \"version\": \"\u003c 5.1.2\"}]}], \"references\": [{\"url\": \"https://github.com/cole/aiosmtplib/security/advisories/GHSA-vxj7-4xrp-5vr4\", \"name\": \"https://github.com/cole/aiosmtplib/security/advisories/GHSA-vxj7-4xrp-5vr4\", \"tags\": [\"x_refsource_CONFIRM\"]}, {\"url\": \"https://github.com/cole/aiosmtplib/commit/9fab7ba1361dbf7622ede1315a24be805cff09c9\", \"name\": \"https://github.com/cole/aiosmtplib/commit/9fab7ba1361dbf7622ede1315a24be805cff09c9\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/cole/aiosmtplib/releases/tag/v5.1.2\", \"name\": \"https://github.com/cole/aiosmtplib/releases/tag/v5.1.2\", \"tags\": [\"x_refsource_MISC\"]}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"aiosmtplib is an asynchronous SMTP client for use with asyncio. Prior to 5.1.2, SMTPProtocol.start_tls in src/aiosmtplib/protocol.py consumes the server\u0027s 220 response and starts the TLS handshake without clearing SMTPProtocol._buffer. An active network attacker can place attacker-chosen SMTP response lines after the plaintext 220 response in the same network segment. The method then calls loop.start_tls; those bytes survive the transport upgrade and are parsed as the first response from inside the TLS session, desynchronizing subsequent SMTP command and response pairs. Connections using start_tls=True or opportunistic STARTTLS are affected, while connections using use_tls=True are not. This issue is fixed in version 5.1.2.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-74\", \"description\": \"CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component (\u0027Injection\u0027)\"}]}], \"providerMetadata\": {\"orgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"shortName\": \"GitHub_M\", \"dateUpdated\": \"2026-08-20T14:29:58.580Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-55558\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-20T20:00:21.869Z\", \"dateReserved\": \"2026-06-16T23:11:20.213Z\", \"assignerOrgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"datePublished\": \"2026-08-20T14:29:58.580Z\", \"assignerShortName\": \"GitHub_M\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}