{"id":"PYSEC-2026-4165","summary":"social-auth-core: VK App backend accepts unsigned callback data when auth_key is missing","details":"### Impact\n\nThe `vk-app` backend accepted VK application callback data without verifying the callback signature when the `auth_key` parameter was omitted.\n\nApplications using this backend could treat unsigned attacker-controlled data as a verified VK identity. An attacker could choose callback fields such as `viewer_id`, `access_token`, `api_id`, and `api_result`, potentially allowing authentication as an arbitrary VK user ID.\n\nThe issue affects only applications using the `vk-app` backend.\n\n### Patches\n\nThe issue has been fixed by requiring `auth_key` to be present and valid before callback data is trusted.\n\nUsers should upgrade to a patched version.\n\nFix:\n\n* https://github.com/python-social-auth/social-core/pull/1811\n\n### Workarounds\n\nApplications that cannot upgrade immediately should disable the `vk-app` backend by removing `social_core.backends.vk.VKAppOAuth2` from `SOCIAL_AUTH_AUTHENTICATION_BACKENDS`.\n\nThere is no complete workaround while continuing to use the vulnerable backend.\n\n### Credits\n\nReported by @lalalala5678 through GitHub private vulnerability reporting.","aliases":["CVE-2026-57178","GHSA-3c93-f73f-qc9h"],"modified":"2026-10-01T17:45:17.846162070Z","published":"2026-10-01T16:38:39.761759Z","references":[{"type":"WEB","url":"https://github.com/python-social-auth/social-core/security/advisories/GHSA-3c93-f73f-qc9h"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-57178"},{"type":"WEB","url":"https://github.com/python-social-auth/social-core/pull/1811"},{"type":"WEB","url":"https://github.com/python-social-auth/social-core/commit/1bfacdd0379e5eb46e169a99ab648b835e9bb6a2"},{"type":"PACKAGE","url":"https://github.com/python-social-auth/social-core"},{"type":"WEB","url":"https://github.com/python-social-auth/social-core/releases/tag/5.0.0"},{"type":"PACKAGE","url":"https://pypi.org/project/social-auth-core"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-3c93-f73f-qc9h"}],"affected":[{"package":{"name":"social-auth-core","ecosystem":"PyPI","purl":"pkg:pypi/social-auth-core"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.0.0"}]}],"versions":["0.0.1","0.1.0","0.2.0","0.2.1","1.0.0","1.0.1","1.1.0","1.2.0","1.3.0","1.4.0","1.5.0","1.6.0","1.7.0","2.0.0","3.0.0","3.1.0","3.2.0","3.3.0","3.3.1","3.3.2","3.3.3","3.4.0","4.0.2","4.0.3","4.1.0","4.2.0","4.3.0","4.4.0","4.4.1","4.4.2","4.5.0","4.5.1","4.5.2","4.5.3","4.5.4","4.5.5","4.5.6","4.6.0","4.6.1","4.7.0","4.8.0","4.8.1","4.8.2","4.8.3","4.8.4","4.8.5","4.8.6","4.8.7","4.9.0","4.9.1"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/social-auth-core/PYSEC-2026-4165.yaml"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"}]}