Redis 4.5.5 Vulnerability: CVE-2021-31294 Analysis

by Alex Johnson 51 views

In this article, we'll delve into a medium severity vulnerability identified in the redis-4.5.5-py3-none-any.whl library, a Python client for the Redis database. This vulnerability, tracked as CVE-2021-31294, has a CVSS score of 5.9 and could potentially lead to a denial-of-service (DoS) condition. Understanding the details of this vulnerability is crucial for developers and system administrators who rely on Redis in their applications.

Understanding the Vulnerability

The vulnerability, CVE-2021-31294, affects Redis versions prior to a specific fix implemented in 2021 for versions 6.2.x and 7.x. It stems from a flaw that allows a malicious replica to trigger an assertion failure on the primary Redis server. This is achieved by sending a non-administrative command, specifically a SET command, during replication. While older versions of Redis (prior to 6.2) weren't designed with specific safety measures against this type of attack, understanding the vulnerability is essential for maintaining the stability and reliability of your Redis deployments.

The core issue lies in the interaction between a primary Redis server and its replicas. Redis replicas are designed to synchronize data from the primary server, ensuring data consistency across the cluster. However, this vulnerability exploits a loophole in the command processing logic during replication. By sending a crafted SET command, an attacker can cause the primary server to enter an unexpected state, leading to an assertion failure and subsequent service disruption. An assertion failure is a condition where the program's assumptions about its internal state are violated, causing it to terminate abruptly.

Technical Details

To understand the vulnerability better, let's break down the key technical aspects:

  • Affected Library: redis-4.5.5-py3-none-any.whl (Python client for Redis)
  • Vulnerability Identifier: CVE-2021-31294
  • CVSS Score: 5.9 (Medium Severity)
  • Attack Vector: Network
  • Attack Complexity: High
  • Privileges Required: None
  • User Interaction: None
  • Impact: Availability (High)
  • Root Cause: Improper command handling during replication
  • Exploitability: A malicious replica sends a crafted SET command to the primary server.
  • Consequence: Assertion failure on the primary server, leading to denial of service.

Impact Assessment

The impact of CVE-2021-31294 is primarily a denial-of-service (DoS). If exploited successfully, an attacker can disrupt the availability of the Redis service, potentially impacting applications that rely on it. While the vulnerability doesn't directly compromise data confidentiality or integrity, the disruption of service can have significant consequences for businesses and users. The vulnerability's medium severity rating (CVSS 5.9) reflects the potential impact and the relative complexity of exploiting it.

It's important to note that the attack complexity is rated as high. This means that exploiting the vulnerability requires a certain level of technical expertise and a specific set of conditions to be met. The attacker needs to control a Redis replica and craft a malicious SET command that triggers the assertion failure on the primary server. However, once the conditions are met, the attack can be executed without requiring any user interaction or special privileges.

Analyzing the Vulnerability Report

Let's dissect the vulnerability report to gain a comprehensive understanding of the issue.

The report highlights that the vulnerable library is redis-4.5.5-py3-none-any.whl, a Python client for Redis. The library's home page provides additional information and resources: https://files.pythonhosted.org/packages/e0/7f/21a09f8c9f5db6f5e24432f7a0f916ca386025d74e4da6d0f5164aa9a78a/redis-4.5.5-py3-none-any.whl.

The report also specifies the path to the dependency file (/requirements.txt) and the path to the vulnerable library within the file system. This information is useful for identifying the vulnerable component within a project or deployment.

Key Findings from the Vulnerability Report

  • CVE-2021-31294: This is the unique identifier for the vulnerability, allowing you to research it further in vulnerability databases.
  • Medium Severity (CVSS 5.9): Indicates the potential impact and exploitability of the vulnerability.
  • Vulnerable Library: redis-4.5.5-py3-none-any.whl
  • Vulnerability Details: A replica can cause an assertion failure in a primary server by sending a non-administrative command (SET).
  • Fix Information: Fixed in Redis versions 6.2.x and 7.x (in 2021). However, versions before 6.2 were not intended to have safety guarantees related to this.
  • Exploit Maturity: Not Defined (meaning there's no widely available exploit code, but the vulnerability is understood).
  • EPSS (Exploit Prediction Scoring System): 0.2% (a relatively low probability of exploitation in the wild).

The vulnerability report also provides a detailed breakdown of the CVSS v3 score, which is crucial for understanding the technical aspects of the vulnerability. The base score of 5.9 is derived from several metrics, including:

  • Attack Vector (Network): The vulnerability can be exploited over a network.
  • Attack Complexity (High): Exploitation requires specific conditions and technical expertise.
  • Privileges Required (None): No special privileges are needed to exploit the vulnerability.
  • User Interaction (None): No user interaction is required to trigger the vulnerability.
  • Scope (Unchanged): The vulnerability affects the Redis server itself.
  • Confidentiality Impact (None): The vulnerability doesn't directly compromise data confidentiality.
  • Integrity Impact (None): The vulnerability doesn't directly compromise data integrity.
  • Availability Impact (High): The vulnerability can lead to a denial-of-service condition.

Remediation and Mitigation

Given the details of the vulnerability, the primary remediation strategy is to upgrade to a patched version of Redis. If you are using Redis 6.2.x or 7.x, ensure that you have applied the security updates released in 2021 that address this issue. If you are using an older version of Redis (prior to 6.2), upgrading to a more recent and supported version is highly recommended. These older versions do not have safety guarantees related to this vulnerability.

Upgrade to a Patched Version

The most effective way to address this vulnerability is to upgrade your Redis installation to a version that includes the fix for CVE-2021-31294. As the vulnerability report indicates, this issue was resolved in Redis versions 6.2.x and 7.x. Therefore, upgrading to one of these versions or a later release will provide the necessary protection.

To upgrade your Redis installation, follow the instructions provided in the official Redis documentation. The upgrade process may vary depending on your operating system and deployment environment. It is crucial to carefully plan and execute the upgrade to minimize any potential disruption to your applications.

Mitigation Strategies

In scenarios where immediate upgrades are not feasible, consider implementing the following mitigation strategies to reduce the risk of exploitation:

  • Restrict Access to Redis Instances: Limit network access to your Redis instances to only trusted clients and networks. This can be achieved by configuring firewalls and access control lists (ACLs).
  • Monitor Redis Logs: Regularly monitor Redis logs for suspicious activity or error messages that may indicate an attempted exploit. Look for patterns or anomalies that could be related to CVE-2021-31294.
  • Implement Replica Security: If possible, implement security measures to protect your Redis replicas from being compromised. This may involve authentication and authorization mechanisms.

Long-Term Security Practices

In addition to addressing this specific vulnerability, it is essential to adopt long-term security practices to minimize the risk of future issues. These practices include:

  • Regularly Update Dependencies: Keep your Redis client libraries and other dependencies up to date to benefit from security patches and bug fixes.
  • Follow Security Best Practices: Adhere to security best practices for Redis deployments, such as using strong passwords, enabling authentication, and configuring appropriate access controls.
  • Conduct Vulnerability Assessments: Regularly conduct vulnerability assessments of your Redis deployments to identify and address potential security weaknesses.
  • Stay Informed About Security Advisories: Subscribe to security advisories and mailing lists to stay informed about the latest vulnerabilities and security updates for Redis.

Conclusion

CVE-2021-31294 is a medium severity vulnerability affecting the redis-4.5.5-py3-none-any.whl library. It can lead to a denial-of-service condition if exploited successfully. The primary remediation strategy is to upgrade to a patched version of Redis (6.2.x or 7.x). If immediate upgrades are not possible, consider implementing mitigation strategies such as restricting access to Redis instances and monitoring logs for suspicious activity. By understanding the details of this vulnerability and implementing appropriate security measures, you can protect your Redis deployments from potential attacks.

Remember to always stay informed about the latest security vulnerabilities and best practices to ensure the security and stability of your systems.

For more information on Redis security best practices, visit the official Redis security documentation: https://redis.io/docs/security/