Executive Summary

CVE-2026-8890 is an authentication bypass vulnerability in the code100x Mobile API. It occurs because the middleware function `withMobileAuth` only checks for the presence of an `Auth-Key` HTTP header without validating its value. This causes the middleware to skip generating the internal user identity header (`g`).

Attackers can exploit this by supplying a crafted JSON payload in the `g` header, which is trusted by the downstream route handler for the mobile courses endpoint. This allows unauthenticated attackers to impersonate arbitrary users, including administrators, and gain unauthorized access to course data.

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Impact Analysis

This vulnerability can have serious impacts as it allows unauthenticated attackers to bypass authentication and impersonate any user, including administrators.

• Unauthorized access to sensitive course data belonging to any enrolled user or administrator.
• Bypassing standard access controls, leading to potential data leakage.
• Compromise of user privacy and integrity of the system's data.

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Detection Guidance

This vulnerability can be detected by monitoring HTTP requests to the Mobile API endpoints for the presence of the 'Auth-Key' header combined with a crafted 'g' HTTP header containing JSON payloads that spoof user identities.

Specifically, detection involves identifying requests where the 'Auth-Key' header is present but not validated, and the 'g' header contains suspicious or unexpected user identity data.

Commands to detect such activity might include using network traffic inspection tools like tcpdump or Wireshark to filter HTTP headers, or using grep on server logs to find requests with these headers.

• Using tcpdump to capture HTTP headers containing 'Auth-Key' and 'g': tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep -E 'Auth-Key|g:'
• Searching server access logs for suspicious 'Auth-Key' and 'g' headers: grep -i 'Auth-Key' /var/log/nginx/access.log | grep -i 'g='
• Using curl to test the endpoint by sending a crafted 'g' header with a spoofed user identity to see if unauthorized access is granted.

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Mitigation Strategies

Immediate mitigation involves ensuring that the middleware properly validates the 'Auth-Key' header and strips or ignores any client-supplied 'g' headers to prevent user identity spoofing.

Specifically, update the code to remove or sanitize the 'g' header in the `withMobileAuth` middleware function so that downstream handlers do not trust client-supplied user identity headers.

Applying the patch or update that removes the ability to inject or alter the 'g' header during mobile authentication is critical.

• Deploy the fix from the official patch that strips the 'g' header in the middleware.
• Review and audit all API endpoints to ensure they do not trust client-supplied identity headers.
• Monitor logs for suspicious requests containing 'Auth-Key' and 'g' headers until the fix is applied.

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Compliance Impact

The vulnerability allows unauthorized access to sensitive user and administrator course data by bypassing authentication controls. This unauthorized access to personal and potentially sensitive information could lead to non-compliance with data protection regulations such as GDPR and HIPAA, which require strict access controls and protection of personal data.

Specifically, the authentication bypass enables attackers to impersonate arbitrary users and access their data without proper authorization, violating principles of confidentiality and data integrity mandated by these standards.

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