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Use After FreeWeakness · CWE-416

CVE-2025-36854

HIGH · 8.1 CVSS v3.1 Published 2025-09-08
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
90/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A vulnerability ( CVE-2024-38229 https://www.cve.org/CVERecord ) exists in EOL ASP.NET when closing an HTTP/3 stream while application code is writing to the response body, a race condition may lead to use-after-free, resulting in Remote Code Execution. Per CWE-416: Use After Free https://cwe.mitre.org/data/definitions/416.html , Use After Free is when a product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer. This issue affects EOL ASP.NET 6.0.0 <= 6.0.36 as represented in this CVE, as well as 8.0.0 <= 8.0.8, 9.0.0-preview.1.24081.5 <= 9.0.0.RC.1 as represented in  CVE-2024-38229 https://www.cve.org/CVERecord . Additionally, if you've deployed self-contained applications https://docs.microsoft.com/dotnet/core/deploying/#self-contained-deployments-scd  targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed. NOTE: This CVE only represents End Of Life (EOL) software components. The vendor, Microsoft, has indicated there will be no future updates nor support provided upon inquiry.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A race condition in EOL ASP.NET versions (6.0.x, 8.0.x, 9.0.x) occurs when closing an HTTP/3 stream while application code writes to the response body, potentially causing use-after-free that leads to remote code execution.

MitigationSince this is EOL software with no vendor patches, organizations must upgrade to a supported .NET version or implement compensating controls (network segmentation, WAF rules) to mitigate the HTTP/3 vector.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed ASP.NET Core runtime version
    Run 'dotnet --list-runtimes' or check the runtime version in your application's deployment files or hosting environment
    Affected if The runtime version begins with 6.0, 8.0, or 9.0 (any x in 6.0.x, 8.0.x, 9.0.x)
  2. Determine if HTTP/3 protocol is enabled in Kestrel
    Inspect your application's 'appsettings.json', 'appsettings.{Environment}.json', or Program.cs for Kestrel server options containing 'HttpProtocols.Http3' or 'protocols: HttpProtocols.Http3'
    Affected if HTTP/3 is explicitly enabled in the Kestrel server configuration
  3. Determine if HTTP/3 is enabled in IIS
    Check IIS manager or the site configuration XML for 'protocols' attribute set to 'h3,h2,http/1.1' or similar containing 'h3'
    Affected if HTTP/3 protocol is enabled at the IIS site level
  4. Verify application writes to HTTP response body
    Review application source code for controllers, middleware, or handlers that perform response body writes (for example, methods returning Content, using Response.WriteAsync, or writing to Response.Body)
    Affected if Application code writes to the HTTP response stream while HTTP/3 is enabled on an affected version

You are affected if you are running ASP.NET Core 6.0.x, 8.0.x, or 9.0.x AND HTTP/3 is enabled AND your application writes to response body during requests.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Since this is EOL software with no vendor patches, organizations must upgrade to a supported .NET version or implement compensating controls (network segmentation, WAF rules) to mitigate the HTTP/3 vector.

Recommended fix High confidence

Migrate to a supported .NET version (currently .NET 8.0 LTS or .NET 9.0 once released)

  1. This CVE specifically covers End of Life (EOL) ASP.NET versions for which Microsoft has explicitly stated no future updates will be provided.
  2. The related CVE-2024-38229 covers the same vulnerability in supported (.NET 8.0 and 9.0) versions with available patches.
  3. For supported versions (8.0.x, 9.0.x), apply the patches as documented in CVE-2024-38229 from Microsoft Security Response Center.
  4. If running EOL versions (6.0.x <= 6.0.36, 8.0.0-8.0.8, 9.0.0-preview.1 to 9.0.0-RC1), migrate to a supported .NET version as soon as possible.
  5. Ensure self-contained applications are recompiled and redeployed after migrating to a supported version.
Caveat Review application compatibility with the target .NET version before migrating; breaking changes may exist between major versions

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation8.0 h
  • Implementation24.0 h
  • Testing16.0 h
  • Review / QA8.0 h
56.0 hours of engineering $9,760
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-36854 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
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  • Version or environment caveats, and links to real fixes
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