# CVE-2026-19874: Konami's Metal Gear Online 3 contains a heap-based buffer overflow

> An attacker can achieve arbitrary code execution in Metal Gear Online 3 by exploiting a heap-based buffer overflow via oversized lobby data fields.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Aug 2026
- **Updated:** 24 Aug 2026
- **Also known as:** GHSA-ggf5-p56j-ccc2

## What is CVE-2026-19874?

CVE-2026-19874 is a critical memory corruption vulnerability in Konami Metal Gear Online 3, published on 24 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A heap-based buffer overflow vulnerability exists in Konami's Metal Gear Online 3, originating from improper validation of lobby data fields related to kicked players. The affected function processes a list of kicked player identifiers using the lobby data key "kick_num" to determine the number of entries, and individual kicked player IDs supplied via keys in the format "kicked_id_%i". The function does not validate that "kick_num" falls within the expected bounds. The game design limits matches to a maximum of 16 players, and the corresponding buffer for storing kicked player IDs is sized accordingly. If "kick_num" exceeds this limit, the function continues writing the provided player IDs past the end of the intended buffer and into adjacent memory regions. These adjacent regions contain Steam callback handler structures responsible for processing lobby data updates, lobby messages, and other related events. By supplying an oversized "kick_num" value and appropriate "kicked_id_%i" fields, an attacker can overwrite fields within the callback handler structures, including function pointers and callback argument values. Successful exploitation may enable control-flow hijacking, potentially allowing arbitrary code execution within the game process.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-19874?


## How do I fix CVE-2026-19874?

No fix has been published for CVE-2026-19874 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-19874 being exploited?

There is no known exploitation of CVE-2026-19874 in the wild and no public exploit code.

Public exploit code:

- CVE-2026-19874 (github_poc): https://github.com/alicealys/mgo3-rce

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-19874 and fix it if it is affected.

What it is: CVE-2026-19874 is a critical memory corruption vulnerability in Konami Metal Gear Online 3, published on 24 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-19874 in the wild and no public exploit code.

Affected product: Konami Metal Gear Online 3. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-19874/ (Markdown: https://insights.sbomify.com/CVE-2026-19874/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19874
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19874
- OSV: https://osv.dev/vulnerability/CVE-2026-19874

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-19874/
Summaries are generated and may contain mistakes; the official description above is the record.