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

Advisory record · `GHSA-2cwq-pwfr-wcw3`

- **Identifiers:** `GHSA-2cwq-pwfr-wcw3` · `CVE-2026-44375`
- **State:** Confirmed
- **Severity:** CVSS 7.5 High
- **Critical:** No
- **Weakness (CWE):** [CWE-789](https://cwe.mitre.org/data/definitions/789.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 6 May 2026
- **Updated:** 14 May 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 6 May 2026, 23:05 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `Nerdbank.MessagePack` (NuGet): affected `<1.1.62`; fixed in `1.1.62`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Nerdbank.MessagePack versions before 1.1.62 are vulnerable. A remote attacker who can supply MessagePack data to an application that deserializes a type containing a DateTime value can send a small payload declaring an oversized timestamp extension length, causing a stack overflow that terminates the process. Upgrade to Nerdbank.MessagePack 1.1.62 or later. If upgrading is not possible, avoid deserializing untrusted input into types with DateTime fields.

Written 9 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 7.5 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0035, the 29th percentile, on 9 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:22 UTC: First seen by agentprime
- 31 Oct 2026, 15:22 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-2cwq-pwfr-wcw3)

## Sources

- [GitHub Advisory Database: GHSA-2cwq-pwfr-wcw3](https://github.com/advisories/GHSA-2cwq-pwfr-wcw3)
- [OSV: GHSA-2cwq-pwfr-wcw3](https://osv.dev/vulnerability/GHSA-2cwq-pwfr-wcw3)
- <https://github.com/AArnott/Nerdbank.MessagePack/security/advisories/GHSA-2cwq-pwfr-wcw3>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-44375>
- <https://github.com/AArnott/Nerdbank.MessagePack/pull/941>
- <https://github.com/AArnott/Nerdbank.MessagePack/commit/7d1eb319cfabe7280e70699946c9a48579fa2f30>
- <https://github.com/AArnott/Nerdbank.MessagePack>
- <https://github.com/AArnott/Nerdbank.MessagePack/releases/tag/v1.1.62>
- <https://github.com/msgpack/msgpack/blob/master/spec.md#timestamp-extension-type>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-2cwq-pwfr-wcw3>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-2cwq-pwfr-wcw3/>. Everything for agents: <https://agentprime.io/llms.txt>.