PYSEC-2026-4165

Vulnerability from pysec - Published: 2026-10-01 16:38 - Updated: 2026-10-01 17:10
VLAI
Details

Impact

The vk-app backend accepted VK application callback data without verifying the callback signature when the auth_key parameter was omitted.

Applications 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.

The issue affects only applications using the vk-app backend.

Patches

The issue has been fixed by requiring auth_key to be present and valid before callback data is trusted.

Users should upgrade to a patched version.

Fix:

  • https://github.com/python-social-auth/social-core/pull/1811

Workarounds

Applications that cannot upgrade immediately should disable the vk-app backend by removing social_core.backends.vk.VKAppOAuth2 from SOCIAL_AUTH_AUTHENTICATION_BACKENDS.

There is no complete workaround while continuing to use the vulnerable backend.

Credits

Reported by @lalalala5678 through GitHub private vulnerability reporting.

Severity
7.4 (High)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Impacted products
Name purl
social-auth-core pkg:pypi/social-auth-core
Aliases
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "social-auth-core",
        "purl": "pkg:pypi/social-auth-core"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "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"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-57178",
    "GHSA-3c93-f73f-qc9h"
  ],
  "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.",
  "id": "PYSEC-2026-4165",
  "modified": "2026-10-01T17:10:43.798424Z",
  "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"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "social-auth-core: VK App backend accepts unsigned callback data when auth_key is missing"
}



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