Improper Authentication in YunaiV yudao-cloud

Executive Summary

CVE-2026-7679 is a high-severity authentication bypass vulnerability in the yudao-cloud platform, specifically in the getAccessToken() method of the OAuth2TokenServiceImpl.java component.

The flaw allows attackers to use a refresh_token as if it were an access_token to authenticate API requests, bypassing the intended access token mechanism.

This happens because the getAccessToken() method does not properly distinguish between access_token and refresh_token types, enabling unauthorized access to protected resources when a valid refresh_token is provided.

Attackers can exploit this vulnerability remotely by obtaining a refresh_token through methods such as man-in-the-middle attacks, database leaks, or cross-site scripting (XSS).

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Impact Analysis

This vulnerability can allow attackers to bypass authentication controls and gain unauthorized access to protected API endpoints.

By using a refresh_token as an access_token, attackers can impersonate legitimate users and access sensitive data or perform actions without proper authorization.

Such unauthorized access can lead to data breaches, compromise of user accounts, and potential further exploitation of the system.

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Detection Guidance

This vulnerability can be detected by monitoring API requests that use a refresh_token in the Authorization header instead of a proper access_token. Since the flaw allows attackers to authenticate using a refresh_token, inspecting HTTP headers for unusual token usage is key.

A practical detection method is to capture and analyze network traffic to identify Authorization headers containing refresh_tokens. For example, using tools like tcpdump or Wireshark to filter HTTP requests to the affected API endpoints and checking the token format.

• Use tcpdump to capture HTTP traffic on port 80 or 443: tcpdump -i <interface> -A 'tcp port 80 or 443 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
• Use grep or similar tools to search captured logs for Authorization headers containing refresh_token strings.

Additionally, reviewing application logs for authentication attempts using refresh_tokens as access tokens can help detect exploitation attempts.

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Mitigation Strategies

Immediate mitigation involves removing or disabling the fallback logic in the getAccessToken() method that allows refresh_tokens to be accepted as access_tokens.

Implement stricter validation to ensure that only valid access_tokens are accepted for authentication, rejecting any refresh_token used in place of an access_token.

Restrict access to the affected API endpoints and monitor for suspicious authentication attempts using refresh_tokens.

If possible, update or patch the yudao-cloud platform to a version where this vulnerability is fixed.

In the meantime, consider revoking or rotating tokens that might have been compromised, especially refresh_tokens.

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Compliance Impact

This vulnerability allows attackers to bypass authentication by using a refresh_token as an access_token, enabling unauthorized access to protected resources. Such unauthorized access can lead to exposure or compromise of sensitive personal or health data.

As a result, this flaw could negatively impact compliance with data protection regulations such as GDPR and HIPAA, which require strict controls over access to personal and health information to ensure confidentiality and integrity.

Failure to prevent unauthorized access due to this vulnerability may lead to violations of these standards, potentially resulting in legal and financial consequences for affected organizations.

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