CVE-2023-38171 is a high-severity (CVSS 7.5) NULL Pointer Dereference vulnerability in Microsoft.Native.Quic.MsQuic.Schannel. EPSS puts its 30-day exploitation probability at 69.7% (99th percentile). A fix is available for Microsoft.Native.Quic.MsQuic.Schannel — see the affected versions and patch details below.
Remote Denial of Service Vulnerability in Microsoft.Native.Quic.MsQuic.Schannel
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-38171.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2023-38171 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE sits: patch-first territory.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
Microsoft.Native.Quic.MsQuic.Schannel.NETMicrosoft.Native.Quic.MsQuic.OpenSSLReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Impact
The MsQuic server application or process will crash, resulting in a denial of service.
Patches
The following patch was made:
- Don't Allow Version Negotiation Packets for Server Connections - https://github.com/microsoft/msquic/commit/3226cff07d22662f16fc98d605656860e64cd343
Workarounds
Beyond upgrading to the patched versions, there is no other workaround. You must upgrade or disable MsQuic functionality.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Microsoft.Native.Quic.MsQuic.Schannel | all versions | 2.2.3dotnet add package Microsoft.Native.Quic.MsQuic.Schannel --version 2.2.3 |
| .NETNuGet | Microsoft.Native.Quic.MsQuic.OpenSSL | all versions | 2.2.3dotnet add package Microsoft.Native.Quic.MsQuic.OpenSSL --version 2.2.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Microsoft.Native.Quic.MsQuic.Schannel, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Microsoft.Native.Quic.MsQuic.Schannel to 2.2.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-38171 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-38171 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-38171. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2023-38171 in your dependencies?
O3 Security finds CVE-2023-38171 across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.