JSON, JavaScript Object Notation, has become one of the most widely used data exchange formats on the web due to its efficiency and ease of use. Ruby, as a popular and versatile programming language, has a JSON implementation for users to conveniently parse and generate JSON documents. However, a serious vulnerability has been discovered in certain versions of the JSON implementation for Ruby. Designated as CVE-2025-27788, this vulnerability could lead to out of bound reads, often resulting in crashes. In this article, we will discuss the details of this critical vulnerability, its potential impact, and provide guidance on how to address it.

Affected Versions

The vulnerability affects JSON implementations for Ruby starting with version 2.10. up to version 2.10.1. If you are using a version prior to 2.10., your JSON implementation is not vulnerable. The problem has been fixed in the latest version, 2.10.2. Make sure to update your JSON implementation as soon as possible to avoid any potential issues.

Vulnerability Details

Specialized crafted JSON documents can exploit an out of bound read vulnerability when parsed by the Ruby JSON implementation between versions 2.10. and 2.10.1. While handling large JSON arrays, these versions of the JSON parser do not correctly validate the indexes provided, thus leading to out of bound reads. This often results in crashes, which could be potentially exploited by a malicious user to cause a Denial of Service (DoS) attack.

The following code snippet illustrates how this CVE-2025-27788 vulnerability could be exploited

require 'json'

malicious_document = <<-EOM
[
  , 1, 2, 3, 4, 5, 6, 7, 8, 9,
  ...
  983040
]
EOM

JSON.parse(malicious_document) # triggers out of bound read vulnerability

When the JSON parser encounters the malicious_document containing a JSON array with a large number of elements, it will cause an out of bound read, leading to a crash. The example code is provided for educational purposes only, and should NOT be used for malicious intents.

The vulnerability has been officially documented by the Common Vulnerabilities and Exposures (CVE) program, and is given the identifier CVE-2025-27788. You can find the official CVE entry at this link: NVD - CVE-2025-27788

The Ruby JSON implementation project repository and the specific commit that fixes this vulnerability can be found on GitHub:

- Ruby JSON GitHub Repository
- CVE-2025-27788 Fix Commit

What to Do Next

No known workarounds are available for this vulnerability, so it is crucial to update your Ruby JSON implementation to the latest version (2.10.2) as soon as possible. Updating will provide immediate protection against any potential exploitation of the CVE-2025-27788 vulnerability. To update, simply run the following command in your system:

gem update json

After updating, ensure that your Ruby JSON implementation is at version 2.10.2 by running the following code snippet:

require 'json'
puts JSON::VERSION # should display 2.10.2

Conclusion

CVE-2025-27788 is a critical vulnerability that affects the Ruby JSON implementation between versions 2.10. and 2.10.1. Causing out of bound reads and potential crashes, the vulnerability could be exploited by a carefully crafted JSON document. To protect yourself, it is crucial to update to version 2.10.2, which fixes the problem. Stay informed and proactive to ensure the safety and stability of your codebase.

Timeline

Published on: 03/12/2025 14:15:16 UTC
Last modified on: 04/02/2025 12:35:54 UTC