Bug 2540600 (CVE-2026-57178)

Summary: CVE-2026-57178 social-auth-core: social-auth-core: Authentication bypass via missing signature verification in VK App backend
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: dschmidt, ikhan, jlanda, jmitchel, jwong, kshier, omaciel, rbobbitt, simaishi, stcannon, ttakamiy, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in social-auth-core. The VK application backend accepts callback data without verifying its cryptographic signature when the authentication key parameter is omitted. A remote attacker can exploit this vulnerability by submitting crafted callback requests with forged identity parameters, allowing them to bypass authentication and impersonate arbitrary users.
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Description OSIDB Bzimport 2026-09-24 17:33:17 UTC 
Python Social Auth is a social authentication/registration mechanism. Prior to version 5.0.0, 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. The issue has been fixed in version 5.0.0 by requiring `auth_key` to be present and valid before callback data is trusted.