# CVE-2026-48512: MessagePack-CSharp: JSON conversion APIs can recurse without consistent depth enforcement

> Attackers can cause a stack overflow and crash the application by sending deeply nested or malformed JSON to MessagePack-CSharp's conversion APIs.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:H/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:** 22 Jun 2026
- **Updated:** 25 Jun 2026
- **Also known as:** ECHO-1db0-dd7e-7fae, GHSA-cj9g-3mj2-g8vv

## What is CVE-2026-48512?

CVE-2026-48512 is a medium-severity denial of service vulnerability in MessagePack-CSharp, published on 22 Jun 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 2.5.301 and 3.1.7, MessagePack-CSharp's JSON conversion helpers contain multiple recursion paths that do not consistently enforce a depth limit. These paths are in the JSON conversion component rather than normal typed MessagePack deserialization. MessagePackSerializer.ConvertFromJson recursively processes nested JSON arrays and objects in FromJsonCore() without consulting MessagePackSecurity.MaximumObjectGraphDepth. TinyJsonReader.ReadNextToken() recursively consumes comma and colon separator characters, allowing even malformed JSON with long separator runs to consume one stack frame per character. MessagePackSerializer.ConvertToJson applies depth checks to arrays and maps, but the typeless extension branch for ext-100 recursively calls ToJsonCore() without applying MessagePackSecurity.DepthStep(ref reader). Each path can allow attacker-controlled input to exhaust the process stack and trigger an uncatchable StackOverflowException instead of failing with a catchable parse or serialization exception.  This vulnerability is fixed in 2.5.301 and 3.1.7.

Weakness: CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2026-48512?

4 open source packages ship an affected version, including MessagePack. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `MessagePack` | NuGet | All versions | 2.5.301 |
| `MessagePack` | NuGet | All versions | 2.5.301 |
| `MessagePack` | NuGet | From 3.0 | 3.1.7 |
| `MessagePack` | NuGet | From 3.0 | 3.1.7 |

Products: Messagepack Messagepack.

## How do I fix CVE-2026-48512?

Upgrade MessagePack to a fixed version for your release line: 2.5.301 or 3.1.7.

## Is CVE-2026-48512 being exploited?

There is no known exploitation of CVE-2026-48512 in the wild and no public exploit code.

## Other vulnerabilities in MessagePack-CSharp

- [CVE-2026-48109](https://insights.sbomify.com/CVE-2026-48109/): MessagePack-CSharp: LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input (high 8.2)
- [CVE-2026-48502](https://insights.sbomify.com/CVE-2026-48502/): MessagePack-CSharp: Denial of service vulnerabilities can swamp the CPU or crash the process with stack and heap overflows (high 8.2)
- [CVE-2026-48506](https://insights.sbomify.com/CVE-2026-48506/): MessagePack-CSharp: MessagePackReader.Skip can recurse without enforcing maximum object graph depth (high 7.5)
- [CVE-2026-48509](https://insights.sbomify.com/CVE-2026-48509/): MessagePack-CSharp: ASP.NET Core MessagePackInputFormatter defaults to TrustedData for HTTP request bodies (medium 6.3)
- [CVE-2026-48510](https://insights.sbomify.com/CVE-2026-48510/): MessagePack-CSharp: LZ4 decompression allocates from unbounded declared output lengths (medium 6.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-48512 and fix it if it is affected.

What it is: CVE-2026-48512 is a medium-severity denial of service vulnerability in MessagePack-CSharp, published on 22 Jun 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-2026-48512 in the wild and no public exploit code.

Affected packages and fixed versions:
- MessagePack (NuGet): affected all versions; fixed in 2.5.301
- MessagePack (NuGet): affected all versions; fixed in 2.5.301
- MessagePack (NuGet): affected from 3.0; fixed in 3.1.7
- MessagePack (NuGet): affected from 3.0; fixed in 3.1.7

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-2026-48512/ (Markdown: https://insights.sbomify.com/CVE-2026-48512/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-48512
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-48512
- OSV: https://osv.dev/vulnerability/CVE-2026-48512

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-48512/
Summaries are generated and may contain mistakes; the official description above is the record.