Threat Level: green Handler on Duty: Johannes Ullrich

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The danger of sending information for API consumption without adequate security measures

Migrating an on-premise application to the cloud can bring numerous business advantages to companies, among which we have fast deployment times and reusability of functions and decrease complexity in operation and evolution through the use of microservices that are communicated through of the use of API.

During the work of the course for the conformation of incident response teams that I direct at Instituto Tecnológico Metropolitano in Medellín, Colombia, we noticed the following case of a production API: there is an API that is consumed to perform the authentication of a fingerprint that was read through an APP located in a mobile phone. The fingerprint is digitalized using the Wavelet Scalar Quantization (WSQ) Gray-scale Fingerprint Image Compression Algorithm, which is the standard for the exchange of 8-bit, 500ppi fingerprint images, used as well in the criminal justice community. If you have and enforced connection with controls like HTTP Strict Transport Security (HSTS), Perfect Forward Secrecy (PFS) and mutual TLS cert authentication, you will have a strong protection against man-in-the-middle attacks. If not, your connection might be tampered. The following snippet was captured when performing an MITM (snippet truncated for security purposes):

Base64 is not a good choice to hide information. When you decode this information, you get a binary file which is in WSQ format. We will use the NIST Biometric Image Software Mirror located at to decode it and then we have a complete fingerprint that can be used to impersonate the owner's identity (truncated for security purposes):

How can you enforce the confidentiality and integrity of the communication and message?

Manuel Humberto Santander Peláez
SANS Internet Storm Center - Handler

Manuel Humberto Santander Pelaacuteez

194 Posts
ISC Handler
Sep 22nd 2018

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