# CVE-2026-54902: Oj: Use-After-Free in Oj::Parser SAJ Long Key Callback

> A use-after-free vulnerability in the Oj Ruby gem allows attackers to cause a crash or potentially execute code via crafted JSON input.

- **Severity:** Medium 6.3 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 30 Jun 2026
- **Updated:** 1 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-54902, GHSA-m578-w5vf-rfcm, MINI-85hx-8hpm-hp6m, MINI-9f9x-frrg-qgrc, MINI-c47c-825h-73fp, MINI-chh4-pfv9-c7qx, MINI-cx87-9gmx-9xqj, MINI-g47x-fgc7-5mj7, MINI-jfqc-h4gc-xrv7, MINI-jvg9-v369-x9jx, MINI-mf3h-j5vp-qc46, MINI-v58q-j5x6-6m7q, ROOT-APP-RUBY-CVE-2026-54902, UBUNTU-CVE-2026-54902

## What is CVE-2026-54902?

CVE-2026-54902 is a medium-severity use after free vulnerability in ohler55 oj, published on 30 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as a Ruby gem. Prior to version 3.17.2, is vulnerable to Use-After-Free when in SAJ mode. The Oj::Parser does not protect cached object keys (≥ 35 bytes) from garbage collection, and a Ruby callback that triggers GC inside hash_end can cause the key string to be reclaimed while the C parser still holds a pointer to it. The subsequent access to the freed string VALUE results in a segfault, confirmed by an RIP pointing to address 0x4242 (a canary-style pattern suggesting control over the freed memory's content). This issue has been fixed in version 3.17.2.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-54902?

2 open source packages ship an affected version, including oj.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `oj` | RubyGems | All versions | 3.17.3 |
| `oj` | RubyGems | All versions | 3.17.3 |

## How do I fix CVE-2026-54902?

Upgrade oj to 3.17.3 or later.

## Is CVE-2026-54902 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54902 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54902 and fix it if it is affected.

What it is: CVE-2026-54902 is a medium-severity use after free vulnerability in ohler55 oj, published on 30 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54902 exists.

Affected packages and fixed versions:
- oj (RubyGems): affected all versions; fixed in 3.17.3
- oj (RubyGems): affected all versions; fixed in 3.17.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-54902/ (Markdown: https://insights.sbomify.com/CVE-2026-54902/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54902
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54902
- OSV: https://osv.dev/vulnerability/CVE-2026-54902

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54902/
Summaries are generated and may contain mistakes; the official description above is the record.