CAPEC-461

Standard Abstraction Level
Meta — Very abstract, high-level category
Standard — Specific enough to understand
Detailed — Tied to specific technique Draft MITRE CAPEC Status
Stable — Fully reviewed and complete
Draft — Under development
Incomplete — Partially defined
Deprecated — No longer recommended
Obsolete — Replaced by another CAPEC Severity: High
Web Services API Signature Forgery Leveraging Hash Function Extension Weakness

Description

An adversary utilizes a hash function extension/padding weakness, to modify the parameters passed to the web service requesting authentication by generating their own call in order to generate a legitimate signature hash (as described in the notes), without knowledge of the secret token sometimes provided by the web service.

Prerequisites

Web services check the signature of the API calls

Authentication tokens / secrets are shared between the server and the legitimate client

The API call signature is generated by concatenating the parameter list with the shared secret and hashing the result.

An iterative hash function like MD5 and SHA1 is used.

An attacker is able to intercept or in some other way gain access to the information passed between the legitimate client and the server in order to retrieve the hash value and length of the original message.

The communication channel between the client and the server is not secured via channel security such as TLS

Mitigations

Design: Use a secure message authentication code (MAC) function such as an HMAC-SHA1

Skills Required

[Medium] Medium level of cryptography knowledge, specifically how iterative hash functions work. This is needed to select proper padding.