# CVE-2026-54898: Oj: Use-After-Free in Oj::Parser SAJ Callback via Input Mutation

> A use-after-free vulnerability in the Oj Ruby gem allows attackers to execute arbitrary code or cause denial of service via crafted JSON input.

- **Severity:** Low 2.1 (`CVSS:4.0/AV:L/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:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 30 Jun 2026
- **Updated:** 1 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-54898, GHSA-q2gm-54r6-8fwm, MINI-3832-5v48-3724, MINI-82hq-3wfg-ww4q, MINI-8m6f-r894-q979, MINI-9v4w-m9qp-gj88, MINI-c98h-4j8x-7gf8, MINI-grwf-p35c-g75j, MINI-jrq8-c5r8-3926, MINI-jvwr-mvqr-g59c, MINI-m74x-vfw5-ffm8, MINI-vjj6-fr5r-r466, UBUNTU-CVE-2026-54898

## What is CVE-2026-54898?

CVE-2026-54898 is a low-severity use after free vulnerability in ohler55 oj, published on 30 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Oj (Optimized JSON) is a JSON parser and Object marshaller packaged as a Ruby gem. In versions prior to 3.17.2,Oj::Parser#parse is vulnerable to a heap use-after-free when a SAJ/SAJ2 callback mutates the input JSON string during parsing. The C engine holds a raw const byte * pointer into the Ruby string's internal buffer. If a callback (e.g. hash_start) resizes the string — for example by calling String#replace with a longer value — Ruby reallocates the string buffer and frees the old one. The C parser's pointer is left dangling; the next character read at parser.c:607 is a use-after-free. This issue has been fixed in version 3.17.2.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-54898?

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-2026-54898?

Upgrade oj to 3.17.3 or later.

## Is CVE-2026-54898 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54898 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54898 and fix it if it is affected.

What it is: CVE-2026-54898 is a low-severity use after free vulnerability in ohler55 oj, published on 30 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54898 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-2026-54898/ (Markdown: https://insights.sbomify.com/CVE-2026-54898/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54898
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54898
- OSV: https://osv.dev/vulnerability/CVE-2026-54898

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54898/
Summaries are generated and may contain mistakes; the official description above is the record.