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High, CVSS 7.5amended

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

CVE-2026-118747GHSA-vmv3-wvjp-wqpj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (system.formats.cbor 11.0.0, 10.0.15, 9.0.24, 8.0.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • NuGet system.formats.cbor

    Affected
    >= 8.0.0-0, < 8.0.2>= 9.0.0-0, < 9.0.24>= 10.0.0-0, < 10.0.15>= 11.0.0-0, < 11.0.0
    Fixed in
    8.0.2, 9.0.24, 10.0.15, 11.0.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · 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
EPSS
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

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

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 --- | --- | ---…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from osv record GHSA-vmv3-wvjp-wqpj

  2. Revision 1 · created ·

    Published from ghsa record GHSA-vmv3-wvjp-wqpj

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-118747

Advisory: Microsoft Security Advisory CVE-2026-118747 - .NET Denial of Service Vulnerability
IDs: CVE-2026-118747, GHSA-vmv3-wvjp-wqpj
Record: https://patchnext.com/advisories/cve-2026-118747 (revision 2, source checked 11 Nov 2026, 07:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: system.formats.cbor 11.0.0, 10.0.15, 9.0.24, 8.0.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet system.formats.cbor: affected >= 8.0.0-0, < 8.0.2; >= 9.0.0-0, < 9.0.24; >= 10.0.0-0, < 10.0.15; >= 11.0.0-0, < 11.0.0; fixed in 8.0.2, 9.0.24, 10.0.15, 11.0.0

## Suggested inspection (read-only)
- NuGet system.formats.cbor: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on system.formats.cbor.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-vmv3-wvjp-wqpj (GitHub-reviewed advisory GHSA-vmv3-wvjp-wqpj lists affected ranges: NuGet system.formats.cbor >=8.0.0-0 =9.0.0-0 =10.0.0-0 =11.0.0-0 <11.0.0)
- Verified: https://osv.dev/vulnerability/GHSA-vmv3-wvjp-wqpj (OSV record GHSA-vmv3-wvjp-wqpj lists affected ranges: NuGet system.formats.cbor >=8.0.0-0 =9.0.0-0 =10.0.0-0 =11.0.0-0 <11.0.0 (fixed))

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