Ruby JSON up to 2.21.1 Resumable Parser partial_value use after free

Summaryinfo

A vulnerability labeled as problematic has been found in Ruby JSON up to 2.21.1. Affected by this vulnerability is the function partial_value of the component Resumable Parser. Such manipulation leads to use after free. This vulnerability is listed as CVE-2026-71847. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability was found in Ruby JSON up to 2.21.1 and classified as problematic. Affected by this issue is the function partial_value of the component Resumable Parser. The manipulation with an unknown input leads to a use after free vulnerability. Using CWE to declare the problem leads to CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. Impacted is integrity, and availability. CVE summarizes:

Ruby JSON is a JSON implementation for Ruby. From 2.20.0 until 2.21.2, Ruby's JSON native C extension clears the consumed JSON::ResumableParser input buffer but leaves state.start, state.cursor, and state.end pointing into released storage. When partial_value reconstructs an incomplete object containing duplicate keys, the duplicate-key warning path calls cursor_position, which dereferences those stale pointers. This results in a heap-use-after-free and can terminate the Ruby process. An attacker who can supply JSON stream data to an application using JSON::ResumableParser may cause process termination when the application calls partial_value on incomplete attacker-controlled input containing duplicate object keys. This issue has been fixed in version 2.21.2.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-71847 since 08/07/2026. The exploitation is known to be easy. The attack may be launched remotely. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 333382 (Linux Distros Unpatched Vulnerability : CVE-2026-71847), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 2.21.2 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (333382). Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• Programming Language Software

Vendor

• Ruby

Name

• JSON

Version

• 2.21.0
• 2.21.1

License

• open-source

Website

• Product: https://github.com/ruby/json/

CPE 2.3info

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CPE 2.2info

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Once again VulDB remains the best source for vulnerability data.

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