CVE-2026-57178 in Python Social Auth
Summary
by MITRE • 09/24/2026
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.
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Analysis
by VulDB Data Team • 09/24/2026
Python Social Auth serves as a widely utilized framework for implementing social authentication and registration mechanisms within web applications, allowing users to log in using credentials from third-party providers such as VKontakte. The vulnerability identified in versions prior to 5.0.0 specifically impacts the vk-app backend integration, which is designed to handle callbacks from VK application endpoints. This particular implementation flaw stems from an insufficient verification of callback data integrity when specific security parameters are absent from the incoming request payload.
The core technical deficiency lies in the logic governing the validation of authentication tokens received via HTTP callbacks. Specifically, when the auth_key parameter is omitted from the callback data sent by the VK server or a simulated client, the backend fails to verify the cryptographic signature associated with the callback. In secure implementations, every callback should be validated against a shared secret or public key to ensure it originated from the legitimate provider and has not been tampered with during transit. By skipping this verification step when auth_key is missing, the application effectively trusts any data structure presented as valid VK identity information, regardless of its authenticity.
This lack of input validation creates a severe authentication bypass vulnerability that allows an attacker to forge callback responses. An adversary can construct malicious HTTP requests containing arbitrary values for critical fields such as viewer_id, access_token, api_id, and api_result. Since the application does not verify these fields against VK's official signature mechanism in this specific scenario, it accepts the forged data at face value. Consequently, an attacker can manipulate the viewer_id field to impersonate any existing user within the VK ecosystem, thereby gaining unauthorized access to their account on the vulnerable web application without possessing valid credentials or multi-factor authentication factors.
The operational impact of this vulnerability is significant for organizations relying on social login functionality. Successful exploitation enables identity spoofing, which may lead to privilege escalation if the targeted victim holds elevated permissions within the target system. Furthermore, it facilitates unauthorized access to sensitive user data associated with the impersonated account and can be leveraged for further attacks such as session hijacking or malicious actions performed under the guise of a legitimate user. The scope is limited strictly to applications that explicitly configure and utilize the vk-app backend; other social authentication backends within Python Social Auth are not affected by this specific flaw, although they may have their own distinct security considerations.
Mitigation strategies primarily involve upgrading the Python Social Auth library to version 5.0.0 or later, where the developers addressed this issue by enforcing strict validation requirements. In the patched versions, the system mandates that the auth_key parameter must be present and cryptographically valid before any callback data is processed or trusted. For organizations unable to upgrade immediately due to compatibility constraints, a temporary workaround involves implementing custom middleware or overriding the backend logic to manually verify VK signature hashes using the application secret key for all incoming callbacks, ensuring that no unsigned or unverified data reaches the authentication handler regardless of parameter presence.
From a classification perspective, this vulnerability aligns with CWE-287, which describes Improper Authentication, as the system fails to correctly establish the identity of an entity claiming to be legitimate. It also relates closely to CWE-345, Insufficient Verification of Data Authenticity, highlighting the failure to validate data integrity against a trusted source. In terms of offensive security frameworks like MITRE ATT&CK, this flaw supports techniques associated with Account Manipulation and Initial Access through credential-based attacks or social engineering facilitated by forged identity tokens, allowing attackers to bypass standard authentication controls effectively.