How severe is CVE-2023-38171?

CVE-2023-38171 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2023-38171?

CVE-2023-38171 affects the following packages: Microsoft.Native.Quic.MsQuic.Schannel (NuGet), Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet). Ecosystems affected: NuGet.

How do I fix CVE-2023-38171?

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.

How do I detect CVE-2023-38171 in my NuGet dependencies?

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.

How do I mitigate CVE-2023-38171 if there is no patch (or I can't update yet)?

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.

Is CVE-2023-38171 actively exploited in the wild?

No public exploit code has been indexed for CVE-2023-38171 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2023-38171?

CVE-2023-38171 has an EPSS (Exploit Prediction Scoring System) score of 71.0%, placing it in the 99th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

What type of vulnerability is CVE-2023-38171?

CVE-2023-38171 is classified as NULL Pointer Dereference (CWE-476). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2023-38171 published, and has it been updated?

CVE-2023-38171 was published on October 10, 2023 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

.NET

.NET NuGet

Not in CISA KEV

HIGH severity

CVE-2023-38171 — Microsoft.Native.Quic.MsQ…

HIGHFix: microsoft/msquic@3226cff

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 71.0% (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

Also known asBIT-dotnet-2023-38171BIT-dotnet-sdk-2023-38171GHSA-xh5m-8qqp-c5x7

Published

Oct 10, 2023

Updated

Oct 24, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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

via FIRST.org ↗

71.0%probability of exploitation in next 30 days

Very High Risk0.00%

Lower risk than most CVEs99th percentile — riskier than 99% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected

.NETMicrosoft.Native.Quic.MsQuic.Schannel.NETMicrosoft.Native.Quic.MsQuic.OpenSSL

Real-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

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
.NETNuGet	`Microsoft.Native.Quic.MsQuic.Schannel`	all versions	2.2.3`dotnet add package Microsoft.Native.Quic.MsQuic.Schannel --version 2.2.3`
.NETNuGet	`Microsoft.Native.Quic.MsQuic.OpenSSL`	all versions	2.2.3`dotnet add package Microsoft.Native.Quic.MsQuic.OpenSSL --version 2.2.3`

Affected Products

4 products · 7 configurations

Application

.netmicrosoft

≥ 7.0.0 && < 7.0.12

range

Application

visual studio 2022microsoft

≥ 17.7.0 && < 17.7.5

range

windows 11 22h2microsoft

< 10.0.22621.2428

range

windows server 2022microsoft

all

Detection & mitigation playbook

Open-source dependency

Detect
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.

Frequently Asked Questions

### 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.