# CVE-2026-105794: Microsoft MsQuic hostname validation bypass

Source: https://junglewise.ai/threats/cve-2026-105794-msquic-is-a-cross-platform-c-implementation-of-the-ietf-quic  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-06. Updated: 2026-10-06  
License: CC BY 4.0 with a link back

CVE-2026-105794 · Severity: critical · CVSS 4 · Published 2026-10-06

MsQuic is Microsoft's QUIC protocol implementation used in applications and services to enable modern encrypted network connections. When using OpenSSL or QuicTLS backends, the library failed to verify that server certificates matched the intended hostname, allowing an attacker on the network to intercept connections and impersonate servers. The Schannel backend was not affected.

Technologies: [Microsoft MsQuic](https://junglewise.ai/threats/technologies/msquic), [Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet)](https://junglewise.ai/threats/technologies/microsoft-native-quic-msquic-openssl). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft), [NuGet](https://junglewise.ai/threats/vendors/nuget).

## Quick answers

**Is CVE-2026-105794 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-105794 being exploited in the wild.

**How severe is CVE-2026-105794?** Critical severity, with a CVSS score of 4, published 6 October 2026.

**Which products and versions are affected?** Microsoft MsQuic prior to 2.4.20, 2.5.11, and 2.6.1; Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet) ECOSYSTEM:introduced=0,fixed=2.4.20.

**Is there a fix for CVE-2026-105794?** Yes. Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet): upgrade to 2.4.20 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-105794 attacked?** It is attacked over the network or from the adjacent network.

**Am I affected by CVE-2026-105794?** Check whether you run Microsoft MsQuic or Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Microsoft.Native.Quic.MsQuic.OpenSSL (NuGet): upgrade to 2.4.20 or later

  ```sh
  dotnet add package Microsoft.Native.Quic.MsQuic.OpenSSL --version 2.4.20
  ```


## Technical details

MsQuic clients using OpenSSL or QuicTLS TLS backends lack proper hostname validation against server certificates; the X509_VERIFY_PARAM_set1_host and X509_VERIFY_PARAM_set1_ip_asc functions were not being called. An on-path attacker can present a mismatched certificate to spoof the server in a man-in-the-middle attack. The fix ensures the server name from ConnectionStart is validated, falling back to the target IP address if no server name is provided.

## Affected products

- Microsoft MsQuic prior to 2.4.20, 2.5.11, and 2.6.1

## Identifiers

- CVE-2026-105794
- GHSA-w5f4-fx9m-m4q7

## Timeline

- 2026-10-06: disclosed
- 2026-08-28: patched

## References

- [https://github.com/microsoft/msquic/commit/0591586443cc73a2d2cfb679527d91a144b4a412](https://github.com/microsoft/msquic/commit/0591586443cc73a2d2cfb679527d91a144b4a412)
- [https://github.com/microsoft/msquic/commit/508e811370df93e2ad848f5c78347d4fe4f65a91](https://github.com/microsoft/msquic/commit/508e811370df93e2ad848f5c78347d4fe4f65a91)

## Related threats

- [Microsoft QUIC use-after-free in path migration](https://junglewise.ai/threats/cve-2026-62815-microsoft-quic-use-after-free-in-path-migration)
- [Microsoft QUIC use-after-free remote code execution](https://junglewise.ai/threats/microsoft-quic-use-after-free-remote-code-execution-bc730249)
- [MsQuic has a Remote Elevation of Privilege Vulnerability](https://junglewise.ai/threats/cve-2026-32179-msquic-has-a-remote-elevation-of-privilege-vulnerability)
- [Remote Denial of Service Vulnerability in Microsoft QUIC](https://junglewise.ai/threats/remote-denial-of-service-vulnerability-in-microsoft-quic-532bbb6d)
- [MsQuic Remote Denial of Service Vulnerability](https://junglewise.ai/threats/cve-2023-36435-msquic-remote-denial-of-service-vulnerability)