CVE-2026-71847: Ruby JSON

High severity, CVSS 8.7. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Ruby JSON: from 2.20.0, before 2.21.2 (fixed in 2.21.2)

Published 2026-08-07. Last modified 2026-09-18.