A recent update from Microsoft has confirmed issues related to the use of TLS 1.3 as the default protocol in Windows 11, particularly affecting IIS Express when handling client certificates. This problem also extends to full IIS under certain circumstances and stems from TLS 1.3’s incompatibility with a feature known as renegotiation, which allowed servers to request client certificates midway through an encrypted session.
Due to the lack of this feature in TLS 1.3, IIS Express is unable to validate client certificates unless they are requested at the start of the TLS handshake. This limitation affects developers as it complicates testing with mutual TLS (mTLS). Users of earlier Windows 11 builds and Server 2022 have reported connection resets in their browsers, while those using version 24H2 and Server 2025 encounter a 500.0 Internal Server Error with error code 0x80070032, indicating that the request is not supported.
Currently, Microsoft has not provided a permanent fix for this issue, leaving developers in a challenging position. Matt Hamrick, a developer, has suggested several workarounds:
- Disable inbound TLS 1.3 via registry edits to revert to TLS 1.2 for local server sessions.
- Modify http.sys bindings using netsh to ensure that certificates are requested during the initial handshake.
- Remove client certificate requirements from the IIS Express configuration file if feasible.
It’s important to note that some of these methods may require administrative privileges and could be reset with Visual Studio updates. Unlike IIS, which offers more control over site bindings with the Negotiate Client Certificate option, IIS Express has limited capabilities as its bindings are preconfigured by Visual Studio.
Additionally, since many web browsers have not fully adopted the TLS 1.3 extension for post-handshake authentication, this issue highlights both server and client-side challenges. As of now, there has been no indication from Microsoft about when or if a proper fix for IIS Express will be released, leaving developers searching for interim solutions or configuration adjustments until a resolution is provided.
For more detailed information, you can read about this issue here and for explanation of the error code, refer to this link.
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