---
id: "CVE-2026-118747"
page: "https://infrastack.ai/live/CVE-2026-118747"
kind: "vulnerability"
aliases: ["CVE-2026-118747", "GHSA-vmv3-wvjp-wqpj"]
title: "Microsoft Security Advisory CVE-2026-118747 - .NET Denial of Service Vulnerability"
severity: "high"
cvss: 7.5
epss: null
exploited: false
status: "open"
category: "runtime"
products: [{"name": "System.Formats.Cbor", "fixed": ["11.0.0"], "affected": ">= 10.0.0, < 11.0.0", "ecosystem": "nuget"}, {"name": "System.Formats.Cbor", "fixed": ["8.0.2"], "affected": ">= 8.0.0-0, < 8.0.2", "ecosystem": "nuget"}, {"name": "System.Formats.Cbor", "fixed": ["9.0.24"], "affected": ">= 9.0.0-0, < 9.0.24", "ecosystem": "nuget"}, {"name": "System.Formats.Cbor", "fixed": ["10.0.15"], "affected": ">= 10.0.0-0, < 10.0.15", "ecosystem": "nuget"}, {"name": "System.Formats.Cbor", "fixed": ["11.0.0"], "affected": ">= 11.0.0-0, < 11.0.0", "ecosystem": "nuget"}]
ecosystems: ["nuget"]
tags: ["cwe-407", "denial-of-service", "dotnet", "nuget", "runtime", "system-formats-cbor"]
not_affected_if: ["does-not-use-cbor", "no-untrusted-input", "system-formats-cbor-not-referenced"]
published_at: "2026-11-10T19:19:51+00:00"
first_seen_at: "2026-11-10T19:24:55+00:00"
updated_at: "2026-11-10T23:23:58+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-118747", "first_seen_at": "2026-11-10T19:24:55+00:00"}, {"source": "analyst", "url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-118747", "first_seen_at": "2026-11-10T22:59:42+00:00", "cites": ["https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-118747", "https://app.opencve.io/cve/CVE-2026-118747", "https://devblogs.microsoft.com/dotnet/dotnet-and-dotnet-framework-november-2026-servicing-updates/"]}, {"source": "ghsa", "url": "https://github.com/advisories/GHSA-vmv3-wvjp-wqpj", "first_seen_at": "2026-11-10T23:23:58+00:00"}]
exploit_sources: []
---

# Microsoft Security Advisory CVE-2026-118747 - .NET Denial of Service Vulnerability

Link for people: https://infrastack.ai/live/CVE-2026-118747 (this .md is for agents)

Microsoft's CVE record (CWE-407, CVSS 7.5) says inefficient algorithmic complexity in .NET lets an unauthenticated network attacker deny service. The affected component listed is the System.Formats.Cbor package, >= 10.0.0 and < 11.0.0, fixed in 11.0.0. No exploitation or public PoC known.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- nuget:System.Formats.Cbor affected >= 10.0.0, < 11.0.0 fixed 11.0.0
- nuget:System.Formats.Cbor affected >= 8.0.0-0, < 8.0.2 fixed 8.0.2
- nuget:System.Formats.Cbor affected >= 9.0.0-0, < 9.0.24 fixed 9.0.24
- nuget:System.Formats.Cbor affected >= 10.0.0-0, < 10.0.15 fixed 10.0.15
- nuget:System.Formats.Cbor affected >= 11.0.0-0, < 11.0.0 fixed 11.0.0

## How to check

Look for System.Formats.Cbor in your projects: run 'dotnet list package --include-transitive' and look for System.Formats.Cbor 10.x, or search packages.lock.json / *.csproj. Exposed only if your service parses CBOR from untrusted network input. The full MSRC page could not be read; confirm the exact per-runtime servicing versions there.

## Fix

Update System.Formats.Cbor to 11.0.0 or later (per the CVE record). Check the MSRC page for any 10.0.x servicing build.

## Timeline

- 2026-11-10T19:24:55+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-118747
- 2026-11-10T22:59:42+00:00 analyst https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-118747 — Component and range from CVE record via OpenCVE/OffSeq mirrors; MSRC page is JS-only and unreadable, so nothing marked verified. Title changed from generic .NET to the named package. Not in the .NET blog table snippet.
- 2026-11-10T23:23:58+00:00 ghsa https://github.com/advisories/GHSA-vmv3-wvjp-wqpj

## Documents

- [advisory] MSRC CVE-2026-118747 (JS page, not readable by tools; content per CVE record) https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-118747
- [advisory] Maintainer's advisory: github.com https://github.com/dotnet/runtime/security/advisories/GHSA-vmv3-wvjp-wqpj
- [advisory] Maintainer's advisory: api.github.com https://api.github.com/repos/dotnet/runtime/security-advisories/GHSA-vmv3-wvjp-wqpj
- [describes] OpenCVE CVE-2026-118747 (CNA data) https://app.opencve.io/cve/CVE-2026-118747
- [fix] Release: github.com https://github.com/dotnet/runtime/releases/tag/v8.0.2
- [fix] Release: github.com https://github.com/dotnet/runtime/releases/tag/v10.0.15
- [fix] Release: github.com https://github.com/dotnet/runtime/releases/tag/v11.0.0
- [mentions] .NET and .NET Framework November 2026 servicing updates https://devblogs.microsoft.com/dotnet/dotnet-and-dotnet-framework-november-2026-servicing-updates/

## From the sources

## Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in .NET. This advisory provides guidance on updating affected applications and components.

Colliding CBOR map keys can hash-flood uniqueness checks; the fix uses seeded Marvin hashing.

## Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/501

## CVSS Details

- **Version:** 3.1
- **Severity:** High
- **Score:** 7.5 (base score)
- **Vector:** `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C`
- **Weakness:** CWE-407

## Affected Platforms

- **Platforms:** Any supported OS
- **Architectures:** All

## <a name="affected-packages"></a>Affected Packages

The tables list affected package versions and fixed versions. These are independently versioned NuGet packages, not runtime patch versions.

### 8.0 - standalone packages

Package | Affected version | Patched version
--- | --- | ---
[System.Formats.Cbor](https://www.nuget.org/packages/System.Formats.Cbor) | >= 8.0.0-0, < 8.0.2 | 8.0.2

### 9.0 - standalone packages

Package | Affected version | Patched version
--- | --- | ---
[System.Formats.Cbor](https://www.nuget.org/packages/System.Formats.Cbor) | >= 9.0.0-0, < 9.0.24 | 9.0.24

Update 9.0 applications to System.Formats.Cbor 9.0.24; 9.0.23 is not a fix. The fixed 10.0.15 package, which includes a net9.0 target, remains an alternative.

### 10.0 - standalone packages

Package | Affected version | Patched version
--- | --- | ---
[System.Formats.Cbor](https://www.nuget.org/packages/System.Formats.Cbor) | >= 10.0.0-0, < 10.0.15 | 10.0.15

### 11.0 - standalone packages

Package | Affected version | Patched version
--- | --- | ---
[System.Formats.Cbor](https://www.nuget.org/packages/System.Formats.Cbor) | >= 11.0.0-0, < 11.0.0 | 11.0.0

## Advisory FAQ

### <a name="how-affected"></a>How do I know if I am affected?

Check the application's System.Formats.Cbor package reference against the affected ranges above. Updating only the installed runtime does not update this independently referenced package.

### <a name="how-fix"></a>How do I fix the issue?

Update each applicable package reference to its patched version listed above, then rebuild and redeploy the application. Updating only the installed runtime does not update an application's standalone package references.

## Other Information

### Reporting Security Issues

If you have found a potential security issue in a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the [MSRC Researcher Portal](https://msrc.microsoft.com/report/vulnerability/new). Further information can be found in the MSRC [Report an Issue FAQ](https://www.microsoft.com/msrc/faqs-report-an-issue).

Security reports made through MSRC may qualify for the Microsoft .NET Bounty. Details of the Microsoft .NET Bounty Program including terms and conditions are at https://aka.ms/corebounty.

### Support

You can ask questions about this issue on GitHub in the .NET GitHub organization. The main repos are located at https://github.com/dotnet/runtime. The Announcements repo (https://github.com/dotnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the linked discussion issue.

### Disclaimer

The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

### External Links

[CVE-2026-118747](https://www.cve.org/CVERecord?id=CVE-2026-118747)

### Acknowledgements

- Anonymous

### Revisions

V1.0 (November 10, 2026): Advisory published.

---

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