Understanding and Mitigating Open Redirection Vulnerability (CVE-2021–36580) in Webmail/Basic…

In the realm of web security, vulnerabilities can often lead to severe consequences if left unaddressed. One such critical issue is the open redirection vulnerability, exemplified by CVE-2021–36580. This vulnerability is particularly concerning in webmail/basic applications, where it can be exploited to launch sophisticated phishing attacks. In this blog post, we’ll delve into what this vulnerability entails, its potential impacts, and how to safeguard against it.

What is Open Redirection?

Open redirect, also known as an open redirection, is a web application vulnerability that allows an attacker to redirect users to arbitrary external URLs. It occurs when a web application redirects users to a target URL specified in an invalidated or user-controlled parameter.

CVE-2021–36580 refers to a specific instance of open redirection found in certain webmail/basic applications. The flaw arises due to inadequate validation of redirect URLs, enabling attackers to manipulate redirection paths.

An attacker will create a specially crafted GET request with a vulnerable endpoint and the vulnerable parameter redirects to an attacker-controlled domain. So a Legitimate user/employee can be tricked and redirected to an attacker-controlled domain name by successfully exploiting the open redirect vulnerability.

vulnerable subdomain:

https://smtp.REDACTED.com/webmail/basic/?referer=https://evil.com&_c=auth&ctz=120&signup_password&_a%5bsignup%5d=1

https://pop.REDACTED.com/webmail/basic/?referer=https://evil.com&_c=auth&ctz=120&signup_password&_a%5bsignup%5d=1

https://webmail.REDACTED.com/webmail/basic/?referer=https://evil.com&_c=auth&ctz=120&signup_password&_a%5bsignup%5d=1

Crafting the Malicious URL: Attackers create a URL that leverages the open redirection flaw to redirect users from the webmail/basic application to a malicious site. This site is typically designed to resemble a legitimate login page.Phishing Attack Delivery: The attacker sends an email or message containing the malicious URL to a target employee. The message might appear to be from a trusted source, such as an internal IT department or a system alert.

Example: Subject: Urgent: Verify Your Account Information

Dear [Employee Name],

We have detected unusual activity on your account. To ensure your security, please click the link below to verify your login credentials:

https://webmail.REDACTED.com/webmail/basic/?referer=https://evil.com&_c=auth&ctz=120&signup_password&_a%5bsignup%5d=1

Thank you for your prompt attention.

Best regards,
IT Support Team

3. Exploiting the Redirection: When the employee clicks on the link, they are redirected to the phishing page and prompted to enter their credentials. The attacker captures these credentials and gains unauthorized access to sensitive systems.

Increased Risk of Phishing: The primary risk is the facilitation of phishing attacks. Users may be tricked into providing their credentials on a fraudulent page that mimics the legitimate login interface.Credential Theft: Compromised credentials can lead to unauthorized access to email accounts, internal systems, and other sensitive resources.Data Breaches: Unauthorized access may result in data breaches, exposing confidential information and potentially leading to further attacks.Reputation Damage: Successful phishing attacks can damage an organization’s reputation and erode trust among clients and stakeholders.Financial Consequences: Addressing the fallout from credential theft and data breaches can involve significant financial costs, including incident response, legal fees, and regulatory fines.