Single Sign-On (SSO): Potential flaws or vulnerabilities in the implementation

As an application security engineer, your responsibility is to identify and address potential flaws or vulnerabilities in the Single Sign-On (SSO) implementation.

Here’s a flaw diagram from an application security engineer’s perspective, highlighting some potential security weaknesses in the SSO process:

Potential Flaws and Vulnerabilities:

1. Improper Redirects (Open Redirect Vulnerability):

• If the application allows un-sanitised input in the redirect URL, an attacker can craft malicious URLs leading users to phishing or other malicious sites.

Examples of improper redirects issues:

• Redirecting users to a phishing site that looks like a legitimate site in order to steal their login credentials or personal information
• Redirecting users to a site that downloads malware onto their device without their knowledge or consent
• Redirecting users to a site that tricks them into making a payment or giving away sensitive information
• Redirecting users to a site that displays fake error messages or warnings in order to scare them into taking action that is harmful to their device or data
• Redirecting users to a site that is designed to look like a government or financial institution site in order to deceive them into giving away sensitive information
• Redirecting users to a site that injects malicious code into their browser, allowing the attacker to take control of their device or steal their data

2. Weak Authentication Mechanisms:

• If the IDP uses weak authentication methods, such as plain passwords without multi-factor authentication (MFA), it increases the risk of unauthorised access

Examples of weak authentication mechanisms:

• Passwords that are easy to guess or that have been reused across multiple accounts
• Security questions that can be easily answered by an attacker with public information
• Single-factor authentication methods, such as only requiring a password and not a second form of identification
• SMS-based authentication, which can be vulnerable to SIM-swapping attacks
• Weak or common PINs (such as “1234” or “0000”) for mobile devices or other devices with PIN-based authentication
• Biometric authentication that can be easily fooled with fake fingerprints or facial images
• Two-factor authentication methods that rely on SMS messages, which can be intercepted by attackers
• Authentication systems that do not enforce strong password policies (such as requiring a minimum length or a mix of characters)
• Authentication systems that do not lock out users after too many failed login attempts and more.

3. Insecure Communication (Man-in-the-Middle Attack):

• Inadequate transport layer security (e.g., using HTTP instead of HTTPS) could expose the authentication process to interception by attackers.
• To ensure the security of the connection, it is recommended to use secure cipher suites such as TLS_AES_256_GCM_SHA384 or TLS_CHACHA20_POLY1305_SHA256. These cipher suites use strong encryption algorithms and key lengths to protect the data being transmitted and are recommended by security experts.

4. Insufficient Token Validation:

• Lack of proper validation of the security token may allow an attacker to forge or tamper with tokens, leading to unauthorised access.
• When generating tokens, use a cryptographically secure random number generator and ensure that the tokens are sufficiently long and complex.

Examples of insufficient token validation issues:

• Accepting a token without checking its expiration date
• Accepting a token without verifying its signature
• Accepting a token without checking whether it was issued by a trusted authority
• Accepting a token without checking the token’s intended audience
• Accepting a token without verifying that the token was issued for a specific purpose

5. Token Lifetime Issues (Session Hijacking):

• If the token’s expiration time is too long, attackers can potentially steal and reuse the token for an extended period, increasing the risk of session hijacking.
• Revoking long-lived tokens can be difficult, especially if many systems have been authorised to use them.

Examples of token lifetime issues:

• Token expiration: If a token has a short lifespan and expires too quickly, it can cause issues for users who need to use the token for an extended period of time
• Token leakage: If a token is transmitted insecurely or stored in an insecure location, it can be compromised and used by an attacker
• Token revocation: If a user’s access to a resource is terminated, but their token is not revoked, they may still be able to access the resource using the token
• Token replay: If a token is intercepted and replayed by an attacker, they can use the token to access resources even if they have not been authorised to do so
• Token theft: If an attacker gains access to a user’s token, they can use it to impersonate the user and access resources they should not have access to

6. Inadequate Session Management:

• Poor session management practices may lead to session fixation attacks or session hijacking.

Examples of inadequate session management issues:

• Lack of session timeouts: Sessions should expire after a certain period of inactivity, otherwise it leaves the user vulnerable to session hijacking attacks
• Session fixation: In this attack, an attacker sets the session ID value for the user’s session and then tricks the user into using the session ID. The attacker can then hijack the session
• Session hijacking: This occurs when a malicious user gains access to a legitimate user’s session ID and takes control of the session. This can be done through various means such as packet sniffing or cross-site scripting (XSS) attacks
• Session prediction: This occurs when an attacker can guess a valid session ID and use it to access the user’s session
• Session revocation: This occurs when a legitimate user logs out of their session, but the session ID remains active and can be used by an attacker to gain access to the user’s account

7. User Enumeration:

• If the IDP responds differently for existing and non-existing users during authentication, it can enable user enumeration attacks.

8. Missing Single Logout (SLO):

• The lack of SLO support might leave users vulnerable to unauthorised access if they don’t explicitly log out from all applications.

Examples of missing single logout issues:

• When a user logs out from one service provider but remains logged in to another service provider
• When a user logs out from a service provider, but the session is not terminated on the identity provider side
• When a user’s session is terminated on the identity provider side, but the service provider session remains active
• When a user closes their browser without logging out, leaving their session active on both the service provider and identity provider side
• When a user’s session times out on the identity provider side, but the service provider session remains active
• When a user logs out from a service provider, but the identity provider session is not terminated

9. Cross-Site Scripting (XSS):

• If the application fails to sanitise user input or outputs token data without proper escaping, it could lead to XSS attacks.

Examples of Cross-site scripting issues:

• Malicious actors injecting scripts into the SSO login page to steal login credentials
• Redirecting users to a fake login page to steal login credentials
• Injecting scripts into the SSO session cookie to hijack user sessions
• Using XSS to bypass security controls in the SSO implementation and gain access to sensitive data
• Reflected XSS attacks, where an attacker tricks a user into clicking a malicious link that executes a script on the SSO login page and steals login credentials
• Stored XSS attacks, where an attacker injects a script into data stored within the SSO system, such as user profiles or messages, that is then executed when viewed by another user
• DOM-based XSS attacks, where an attacker exploits a flaw in the SSO implementation’s client-side code to execute a script that steals login credentials or other sensitive data

10. Token Leakage:

• If the application inadvertently exposes the token in logs, URLs, or referer headers, it can lead to token leakage.

Examples of token leakage issues:

• When a user copies a session ID or token from a URL and sends it to another user who then uses it to access the original user’s account
• When a website includes a user’s session ID or token in a URL that is then shared or bookmarked, allowing someone else to access the user’s account
• When a website includes a user’s session ID or token in a cookie that is then stolen or intercepted by a third party
• When a user accesses a website over an unsecured connection, allowing an attacker to intercept the user’s session ID or token
• When a user’s session ID or token is stored in plaintext in a database and the database is compromised
• When a website’s server logs are not properly secured and a hacker gains access to them, obtaining user session IDs or tokens

Conclusion

In this post, I aim to emphasise the importance of addressing potential flaws by following security best practices:

1. Conducting security assessments
2. Implementing secure coding practices
3. Using strong authentication mechanisms (such as MFA)
4. Configuring secure communication (HTTPS)
5. Implementing proper token validation and management
6. Ensuring secure session handling throughout the SSO process

Regular security testing and audits are essential to identify and remediate any flaws in the SSO implementation.