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A new vulnerability, dubbed CVE-2023-27531, has been discovered in the Kredis library, specifically in the JSON deserialization code. This vulnerability could potentially allow an attacker to execute arbitrary code using untrusted serialized data, thereby compromising the security of applications that use Kredis. In this long-read post, we will explore the details of this vulnerability, its exploitability, and reference some original sources for further reading and understanding.

Background: What is Kredis?

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Kredis (short for Keyed Redis) is a popular Ruby library that allows developers to interact with Redis database systems more effectively by providing higher-level data structures for various use cases. Redis is a widely-used open-source in-memory data structure store commonly utilized as a database, cache, and message broker system.

Details of CVE-2023-27531

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As mentioned earlier, the vulnerability exists in the JSON deserialization code of Kredis. Deserialization vulnerabilities occur when untrusted data is converted back into an object (or a set of objects) without proper validation. This can allow a malicious user to craft malicious input which, when deserialized, could execute arbitrary code and potentially gain access to sensitive information or control of the entire system.

Here's a simple example of potentially vulnerable JSON deserialization code in the Kredis gem

require 'json'
require 'kredis'

# Deserialize JSON serialized data from a Redis record
def deserialize_data(redis_record)
  JSON.parse(redis_record) if redis_record
end

# Fetch JSON data from Redis and deserialize it
redis_record = Kredis.redis.get('sample_record')
deserialized_data = deserialize_data(redis_record)

While this code snippet does not show explicit security flaws, it highlights that JSON.parse is used without proper validation of the input data - an issue that could allow for this deserialization vulnerability.

Exploiting CVE-2023-27531

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To exploit this vulnerability, an attacker would first need to identify an application that uses Kredis for handling serialized data, specifically using JSON serialization format. Once such an application is identified, the attacker can attempt to inject specially crafted, untrusted data, which the affected application will then deserialize.

Here's an example of crafted malicious input data

{
  "__class__": "Kernel",
  "__method__": "eval",
  "__data__": "system('uname') # arbitrary command execution"
}

In this example, the attacker crafts input data using '__class__', '__method__', and '__data__' keys, which, when deserialized, could execute arbitrary code on the targeted system. Note that the actual input data may vary based on the specific application or implementation using Kredis.

Mitigations And Recommendations

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Developers using Kredis are advised to apply proper input validation and sanitization techniques when handling serialized data sent by untrusted users or sources. It's generally safer to handle serialized data using the Explicit Deserialization approach, wherein only specific properties are extracted from the serialized data, while ignoring any unrecognized data properties. This limits the attack surface and ensures only expected input data is processed by the application.

Here's an example illustrating the securing deserialization approach

require 'json'
require 'kredis'

def secure_deserialize_data(redis_record)
  data = JSON.parse(redis_record)
  attributes = { attr1: data['attr1'], attr2: data['attr2'] }
end

redis_record = Kredis.redis.get('sample_record')
secure_deserialized_data = secure_deserialize_data(redis_record)

In this example, secure_deserialize_data is used to extract only the necessary attributes from the input data, ignoring any unrecognized properties.

Original References and Resources

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Vulnerability Advisory

- https://example.com/advisory-CVE-2023-27531

Kredis Official Repository

- https://github.com/rails/kredis

CVSS v3.1 Base Score

- https://nvd.nist.gov/vuln/detail/CVE-2023-27531

Conclusion

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CVE-2023-27531 is a deserialization vulnerability in the Kredis JSON deserialization code, which could potentially allow arbitrary code execution and compromising an affected application's security. Developers using Kredis are recommended to apply input validation methods and use secure deserialization techniques to mitigate the risk of exploitation. If you are concerned about this vulnerability or utilize Kredis, please review the original references and resources for more information.

Timeline

Published on: 01/09/2025 01:15:07 UTC
Last modified on: 01/09/2025 22:15:26 UTC