CVE-2023-0657: Keycloak Improper Enforcement of Token Types Leading to Unintended Access

A serious vulnerability has been discovered in the widely-used Keycloak authentication and authorization platform. Keycloak, an open-source project backed by Red Hat, is a security service that helps secure web applications, mobile applications, and RESTful web services via Single Sign-On (SSO) and Identity Management. The vulnerability (CVE-2023-0657) is related to improper enforcement of token types when validating signatures locally. An authenticated attacker could potentially exploit this flaw to swap a logout token for an access token and gain unauthorized access to data beyond their permission. This issue exposes applications and services relying on Keycloak to potentially severe security risks.

Vulnerability Details

The problem lies in the way Keycloak implements token type validation when verifying tokens' signatures. Token validation is a crucial aspect of ensuring secure communication between services and applications. When done improperly, it may lead to attackers gaining unauthorized access to sensitive data.

In the case of CVE-2023-0657, Keycloak fails to enforce token types while validating their signatures locally. This means that an attacker with a valid logout token could craft a malicious request, swapping the logout token with an access token and thus breaking the integrity of the authentication mechanism. In turn, the attacker could gain access to resources beyond their intended permissions.

Here's an example of the flawed code snippet

// Keycloak's VerifyToken function (vulnerable version)
public boolean verifyToken(String token) {
  try {
    // ... (omitted code for brevity)

    // Signature validation
    if (!isValidSignature(token)) {
      throw new VerificationException("Invalid token signature");
    }

    // Token type enforcement is missing here

    // Check if the token is expired
    if (isExpired(token)) {
      throw new VerificationException("Token is expired");
    }

    // ... (omitted code for brevity)

    return true;
  } catch (VerificationException e) {
    // Log and return false if anything goes wrong
    log.error("Token verification failed: " + e.getMessage());
    return false;
  }
}

Exploitation

To exploit this vulnerability, an attacker needs to have a valid logout token and beauthenticated. This scenario typically requires a previous successful authentication against the Keycloak server. However, we should never underestimate attackers' ability to bypass these security measures.

Once a valid logout token is obtained, the attacker can craft a malicious request, exchanging the logout token with an access token. This action effectively grants the attacker access to resources outside of their permission scope.

It's worth noting that the success of such an attack depends on the specific configuration and settings of the target environment. However, businesses and developers using Keycloak should treat this vulnerability as a critical issue and apply the necessary patches as soon as possible.

For more information and original details, please refer to the following resources

- CVE-2023-0657 - Keycloak's National Vulnerability Database entry
- Keycloak's GitHub repository
- Keycloak's official documentation

Mitigation

The best course of action to protect your systems against this vulnerability (CVE-2023-0657) is to apply the latest patches provided by the Keycloak project.

To fix the vulnerability, you need to ensure proper enforcement of token types during local signature validation. The updated verifyToken method should look like this:

// Keycloak's VerifyToken function (patched version)
public boolean verifyToken(String token, String expectedTokenType) {
  try {
    // ... (omitted code for brevity)

    // Signature validation
    if (!isValidSignature(token)) {
      throw new VerificationException("Invalid token signature");
    }

    // Enforce token type
    if (!isExpectedTokenType(token, expectedTokenType)) {
      throw new VerificationException("Wrong token type");
    }

    // Check if the token is expired
    if (isExpired(token)) {
      throw new VerificationException("Token is expired");
    }

    // ... (omitted code for brevity)

    return true;
  } catch (VerificationException e) {
    // Log and return false if anything goes wrong
    log.error("Token verification failed: " + e.getMessage());
    return false;
  }
}

Make sure you consistently apply security patches and updates to your systems, as well as follow best practices to minimize the risk of exploitation.

Timeline

Published on: 11/17/2024 11:15:05 UTC
Last modified on: 11/18/2024 17:11:17 UTC