# CVE-2026-92707: MessagePack: Nested arrays can blow past buffer length limits

> Attackers can cause denial of service via excessive memory allocation when deserializing nested arrays in MessagePack for C#.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Oct 2026
- **Updated:** 15 Oct 2026
- **Also known as:** ECHO-2222-717f-2f28, GHSA-qhrr-8q5h-9q3h, UBUNTU-CVE-2026-92707

## What is CVE-2026-92707?

CVE-2026-92707 is a medium-severity denial of service vulnerability in MessagePack-CSharp, published on 15 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.303 and 3.1.9, deserializing attacker-controlled MessagePack data as System.Object through PrimitiveObjectFormatter can cause excessive memory allocation. The formatter allocates an object[] from each declared array length before the configured object-graph depth limit rejects the input, while nested array headers can reuse the same trailing unread bytes to satisfy per-header length validation. A comparatively small payload can therefore keep many large arrays alive at once. When an attacker can submit such data repeatedly, the allocations can cause severe managed-heap pressure, excessive garbage collection, process termination, or loss of service. Exposure requires an application to deserialize untrusted data through the affected formatter path and permit repeated attacker-controlled submissions, such as a reachable ASP.NET Core SignalR hub method with an object parameter and AddMessagePackProtocol() enabled. This issue is fixed in versions 2.5.303 and 3.1.9.

Weakness: CWE-1325 (Improperly Controlled Sequential Memory Allocation)

## Which versions are affected by CVE-2026-92707?

4 open source packages ship an affected version, including MessagePack.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `MessagePack` | NuGet | All versions | 2.5.303 |
| `MessagePack` | NuGet | All versions | 2.5.303 |
| `MessagePack` | NuGet | From 3.0.0 | 3.1.9 |
| `MessagePack` | NuGet | From 3.0.0 | 3.1.9 |

## How do I fix CVE-2026-92707?

Upgrade MessagePack to a fixed version for your release line: 2.5.303 or 3.1.9.

## Is CVE-2026-92707 being exploited?

There is no known exploitation of CVE-2026-92707 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-92707 and fix it if it is affected.

What it is: CVE-2026-92707 is a medium-severity denial of service vulnerability in MessagePack-CSharp, published on 15 Oct 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-2026-92707 in the wild and no public exploit code.

Affected packages and fixed versions:
- MessagePack (NuGet): affected all versions; fixed in 2.5.303
- MessagePack (NuGet): affected all versions; fixed in 2.5.303
- MessagePack (NuGet): affected from 3.0.0; fixed in 3.1.9
- MessagePack (NuGet): affected from 3.0.0; fixed in 3.1.9

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-2026-92707/ (Markdown: https://insights.sbomify.com/CVE-2026-92707/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-92707
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-92707
- OSV: https://osv.dev/vulnerability/CVE-2026-92707

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-92707/
Summaries are generated and may contain mistakes; the official description above is the record.