Improper Error Handling in Capgo Before 12.128.2

Executive Summary

This vulnerability exists in Capgo versions before 12.128.2 in the /private/accept_invitation endpoint. When an invalid magic_invite_string is submitted, the server improperly handles the error by returning an HTTP 500 status code instead of a safer 4xx error. This improper error handling can be exploited by attackers who only need the public key to submit malformed magic_invite_string values, causing server errors and potentially leaking internal processing details.

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Detection Guidance

This vulnerability can be detected by monitoring the /private/accept_invitation endpoint for HTTP 500 Internal Server Error responses triggered by malformed or invalid magic_invite_string values.

An effective detection method is to send crafted requests with invalid magic_invite_string parameters to the endpoint and observe if the server returns HTTP 500 errors instead of safer 4xx errors.

For example, you can use curl commands to test the endpoint:

• curl -X POST https://your-capgo-server/private/accept_invitation -d 'magic_invite_string=invalid_string'
• Check if the response status code is 500 instead of a 4xx error.

Additionally, monitoring server logs for repeated HTTP 500 errors at this endpoint can help identify exploitation attempts.

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Impact Analysis

The impact of this vulnerability includes the possibility for attackers to cause server errors by submitting malformed inputs, which may lead to the exposure of internal processing details. This can aid attackers in gaining insights into the server's inner workings, potentially facilitating further attacks or exploitation.

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Compliance Impact

The vulnerability involves improper error handling that causes the server to return HTTP 500 errors containing sensitive internal processing details when an invalid magic_invite_string is submitted.

This exposure of sensitive information through error messages (classified under CWE-209) could potentially lead to information leakage, which may impact compliance with data protection standards such as GDPR or HIPAA that require safeguarding sensitive data and minimizing information disclosure.

However, the provided information does not explicitly state the direct impact on compliance with these regulations.

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Mitigation Strategies

Immediate mitigation steps include updating Capgo to version 12.128.2 or later, where this vulnerability is fixed.

If updating is not immediately possible, implement input validation on the magic_invite_string parameter to ensure invalid values are rejected early.

Enforce CAPTCHA verification before backend processing to prevent automated exploitation using the public key.

Also, configure the server to return safe 4xx error codes instead of HTTP 500 errors when invalid input is detected, and remove sensitive internal error details from responses.

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