Authentication / Authentication Bypass by Capture-Replay

Web and API


Authentication Bypass by Capture-replay is a class of vulnerability found in web and API applications that allows an attacker to bypass authentication mechanisms by replaying credentials or authentication tokens that were previously captured (CWE-287). The attack is usually executed by intercepting the authentication traffic via man-in-the-middle or by sniffing the network. This type of attack is usually performed on weak authentication mechanisms, such as HTTP Basic and Digest authentication, as well as session tokens (OWASP Testing Guide).


Authentication Bypass by Capture-replay is a serious vulnerability since it can allow an attacker to gain access to protected resources without the need for valid credentials. This type of attack can also be used to gain access to sensitive information, such as user data and passwords, which can be used for further malicious activities. The risk level of this vulnerability is high and should be addressed immediately.


The best way to prevent Authentication Bypass by Capture-replay is to implement strong authentication mechanisms and use secure protocols, such as HTTPS. It is also important to ensure that all authentication tokens are generated securely and that they are not easily intercepted. Additionally, session tokens should be renewed after each successful authentication and should be invalidated after a certain period of time.


Below is an example of an authentication bypass attack using a captured session token (CVE-2019-1003025). In this example, an attacker captures the session token of a user and then uses it to authenticate as the user.

import requests

# Get the session token of the user
r = requests.get("", auth=("username", "password"))
session_token = r.cookies["session_token"]

# Use the captured session token to authenticate
r = requests.get("", cookies={"session_token": session_token})

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