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High, CVSS 7.5amended

Microsoft Security Advisory CVE-2026-96959 - .NET and Visual Studio Denial of Service Vulnerability

CVE-2026-96959GHSA-c399-9853-6jmj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (system.security.cryptography.xml 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.5), 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.security.cryptography.xml

    Affected
    >= 10.0.0, <= 10.0.12>= 11.0.0-preview.1, <= 11.0.0-rc.1>= 8.0.0, <= 8.0.4>= 9.0.0, <= 9.0.20
    Fixed in
    11.0.0-rc.2, 10.0.13, 8.0.5, 9.0.21

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
EPSS
  • CVE-2026-96959: 0.97% estimated exploitation activity in the next 30 days; percentile 61.92 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
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 System.Security.Cryptography.Xml; System.Private.Xml. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. Signed XML fixes add input-depth and operation-count limits, prohibit DTD processing by default, validate entity references, bound encrypted-data candidate processing, and cap attributes and namespaces used by C14N transforms. Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/489 CVSS Details - Version: 3.1 - Severity: High - Score: 7.5 - Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling) Affected Platforms - Platforms: Windows, Linux, macOS - Architectures: All <a name="affected-packages"</aAffected Packages The vulnerability affects Microsoft .NET projects that use an…

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

    Amended from ghsa record GHSA-c399-9853-6jmj

  2. Revision 1 · created ·

    Published from osv record GHSA-c399-9853-6jmj

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-2026-96959

Advisory: Microsoft Security Advisory CVE-2026-96959 - .NET and Visual Studio Denial of Service Vulnerability
IDs: CVE-2026-96959, GHSA-c399-9853-6jmj
Record: https://patchnext.com/advisories/cve-2026-96959 (revision 2, source checked 26 Oct 2026, 17:05 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.security.cryptography.xml 11.0.0-rc.2, 10.0.13, 9.0.21, 8.0.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet system.security.cryptography.xml: affected >= 10.0.0, <= 10.0.12; >= 11.0.0-preview.1, <= 11.0.0-rc.1; >= 8.0.0, <= 8.0.4; >= 9.0.0, <= 9.0.20; fixed in 11.0.0-rc.2, 10.0.13, 8.0.5, 9.0.21

## Suggested inspection (read-only)
- NuGet system.security.cryptography.xml: 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.security.cryptography.xml.
- 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://osv.dev/vulnerability/GHSA-c399-9853-6jmj (OSV record GHSA-c399-9853-6jmj lists affected ranges: NuGet system.security.cryptography.xml >=10.0.0 =11.0.0-preview.1 =8.0.0 =9.0.0 <9.0.21 (fixed))
- Verified: https://github.com/advisories/GHSA-c399-9853-6jmj (GitHub-reviewed advisory GHSA-c399-9853-6jmj lists affected ranges: NuGet system.security.cryptography.xml >=10.0.0 =11.0.0-preview.1 =8.0.0 =9.0.0 <=9.0.20)

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