{
    "CVE_data_meta": {
        "ASSIGNER": "security-advisories@github.com",
        "ID": "CVE-2021-21274",
        "STATE": "PUBLIC",
        "TITLE": "Denial of service attack via .well-known lookups"
    },
    "affects": {
        "vendor": {
            "vendor_data": [
                {
                    "product": {
                        "product_data": [
                            {
                                "product_name": "synapse",
                                "version": {
                                    "version_data": [
                                        {
                                            "version_value": ">=0.99.0, < 1.25.0"
                                        }
                                    ]
                                }
                            }
                        ]
                    },
                    "vendor_name": "matrix-org"
                }
            ]
        }
    },
    "data_format": "MITRE",
    "data_type": "CVE",
    "data_version": "4.0",
    "description": {
        "description_data": [
            {
                "lang": "eng",
                "value": "Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.25.0, a malicious homeserver could redirect requests to their .well-known file to a large file. This can lead to a denial of service attack where homeservers will consume significantly more resources when requesting the .well-known file of a malicious homeserver. This affects any server which accepts federation requests from untrusted servers. Issue is resolved in version 1.25.0. As a workaround the `federation_domain_whitelist` setting can be used to restrict the homeservers communicated with over federation."
            }
        ]
    },
    "impact": {
        "cvss": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "LOW",
            "baseScore": 4.3,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L",
            "version": "3.1"
        }
    },
    "problemtype": {
        "problemtype_data": [
            {
                "description": [
                    {
                        "lang": "eng",
                        "value": "CWE-400 Uncontrolled Resource Consumption"
                    }
                ]
            }
        ]
    },
    "references": {
        "reference_data": [
            {
                "name": "https://github.com/matrix-org/synapse/security/advisories/GHSA-2hwx-mjrm-v3g8",
                "refsource": "CONFIRM",
                "url": "https://github.com/matrix-org/synapse/security/advisories/GHSA-2hwx-mjrm-v3g8"
            },
            {
                "name": "https://github.com/matrix-org/synapse/releases/tag/v1.25.0",
                "refsource": "MISC",
                "url": "https://github.com/matrix-org/synapse/releases/tag/v1.25.0"
            },
            {
                "name": "https://github.com/matrix-org/synapse/pull/8950",
                "refsource": "MISC",
                "url": "https://github.com/matrix-org/synapse/pull/8950"
            },
            {
                "name": "https://github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6",
                "refsource": "MISC",
                "url": "https://github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6"
            },
            {
                "refsource": "FEDORA",
                "name": "FEDORA-2021-a627cfd31e",
                "url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/"
            }
        ]
    },
    "source": {
        "advisory": "GHSA-2hwx-mjrm-v3g8",
        "discovery": "UNKNOWN"
    }
}