What’s Vulnerable › Vulnerabilities

CVE-2026-71847: Ruby JSON: JSON::ResumableParser#partial_value dereferences a freed input buffer and crashes on truncated duplicate-key streams

• Severity: high (CVSS 8.7 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-07 · updated 2026-10-24
• Weakness: CWE-416

Description

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, < 2.21.2

References

• https://github.com/ruby/json/security/advisories/GHSA-9hj4-r449-hfvc
• https://github.com/ruby/json/security/advisories/GHSA-9hj4-r449-hfvc

Get alerted when CVE-2026-71847 or the next vulnerability affects your stack