{
    "dataType": "CVE_RECORD",
    "dataVersion": "5.2",
    "cveMetadata": {
        "cveId": "CVE-2026-55558",
        "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "state": "PUBLISHED",
        "assignerShortName": "GitHub_M",
        "dateReserved": "2026-06-16T23:11:20.213Z",
        "datePublished": "2026-08-20T14:29:58.580Z",
        "dateUpdated": "2026-08-20T20:00:21.869Z"
    },
    "containers": {
        "cna": {
            "title": "aiosmtplib: STARTTLS response injection",
            "problemTypes": [
                {
                    "descriptions": [
                        {
                            "cweId": "CWE-74",
                            "lang": "en",
                            "description": "CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')",
                            "type": "CWE"
                        }
                    ]
                }
            ],
            "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"
                    }
                }
            ],
            "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"
                }
            ],
            "affected": [
                {
                    "vendor": "cole",
                    "product": "aiosmtplib",
                    "versions": [
                        {
                            "version": "< 5.1.2",
                            "status": "affected"
                        }
                    ]
                }
            ],
            "providerMetadata": {
                "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
                "shortName": "GitHub_M",
                "dateUpdated": "2026-08-20T14:29:58.580Z"
            },
            "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's 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."
                }
            ],
            "source": {
                "advisory": "GHSA-vxj7-4xrp-5vr4",
                "discovery": "UNKNOWN"
            }
        },
        "adp": [
            {
                "metrics": [
                    {
                        "other": {
                            "type": "ssvc",
                            "content": {
                                "timestamp": "2026-08-20T20:00:16.093023Z",
                                "id": "CVE-2026-55558",
                                "options": [
                                    {
                                        "Exploitation": "none"
                                    },
                                    {
                                        "Automatable": "no"
                                    },
                                    {
                                        "Technical Impact": "partial"
                                    }
                                ],
                                "role": "CISA Coordinator",
                                "version": "2.0.3"
                            }
                        }
                    }
                ],
                "title": "CISA ADP Vulnrichment",
                "providerMetadata": {
                    "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
                    "shortName": "CISA-ADP",
                    "dateUpdated": "2026-08-20T20:00:21.869Z"
                }
            }
        ]
    }
}