Attack Chain

1. The attacker crafts a malicious HTTP request targeting the Mobile API.
2. The request includes an ‘Auth-Key’ header with an arbitrary value to trigger the bypass condition.
3. The request also includes a ‘g’ HTTP header containing a crafted JSON payload with the attacker’s desired user identity.
4. The middleware in middleware.ts skips identity header generation due to the presence of the ‘Auth-Key’ header.
5. The crafted JSON payload in the ‘g’ header is used to create a spoofed user identity header.
6. The downstream route handler, such as the mobile courses endpoint, trusts the spoofed user identity header.
7. The attacker gains unauthorized access to course data, impersonating the targeted user or administrator.
8. The attacker can then perform actions as the impersonated user, such as viewing, modifying, or deleting course data.

Impact

Successful exploitation of CVE-2026-8890 allows unauthenticated attackers to impersonate any user, including administrators, within the code100x Mobile API. This could lead to unauthorized access to sensitive course data, modification of user accounts, and potential disruption of services. The vulnerability poses a significant risk to the confidentiality, integrity, and availability of the platform. The specific number of affected users is currently unknown, but all users of the code100x Mobile API are potentially at risk.

Recommendation

• Apply the patch or update provided by code100x to address CVE-2026-8890 to remediate the authentication bypass vulnerability.
• Deploy the Sigma rule Detect code100x Mobile API Authentication Bypass Attempt to identify exploitation attempts based on the presence of the ‘Auth-Key’ header and a crafted ‘g’ header.
• Monitor web server logs for HTTP requests containing the ‘Auth-Key’ header in combination with a ‘g’ header, focusing on requests targeting the Mobile API endpoints, as indicated by the rule Detect code100x Mobile API Authentication Bypass Attempt.