Official documentation checked October 14, 2026.
WinHTTP error 12175 means that Windows found a problem with the server’s TLS certificate. It does not, on its own, identify a failed revocation check or prove a Copilot-specific defect. Do not delete trusted roots, disable certificate validation, or remove security updates to make the connection succeed.
1. Identify which certificate check actually failed
Record the exact application and version, destination hostname, time, and complete error text. “Copilot” could mean an organizational Microsoft 365 experience, a personal app, or GitHub Copilot; they do not all use the same client networking implementation. Keep the error’s numeric code and any underlying certificate status together.
Microsoft defines 12175 as ERROR_WINHTTP_SECURE_FAILURE, a general certificate failure. Its separate codes include 12057 for an unavailable revocation check, 12170 for a revoked certificate, 12037 for a certificate validity-date problem, and 12045 for an untrusted root. See the WinHTTP error reference. A revoked certificate must not be treated as merely an unreachable server.
If you maintain the failing application, capture its secure-failure callback details as documented in WINHTTP_STATUS_CALLBACK. End users should supply the existing app diagnostics to support instead of changing registry values based only on the top-level code.
2. Inspect time, certificate chain, and the actual network path
- Check the device clock. Compare the date, time, and time zone with the organization’s time service. An incorrect clock can make an otherwise valid certificate appear expired or not yet valid.
- Have IT inspect the presented certificate. Record its issuer, validity period, and chain for the failing hostname. If an organization-issued certificate appears on a public Microsoft connection, ask whether an approved inspection proxy is involved. An unexpected issuer warrants investigation, not an automatic trust import.
- For a confirmed revocation-retrieval failure, inspect the affected certificate’s actual CRL or OCSP locations. Ask the network/PKI team to check reachability through the same proxy and execution context as the app. A successful browser request to an unrelated Microsoft CRL URL does not test that chain.
- Inspect, but do not reset, WinHTTP configuration. Where the failing component uses WinHTTP, the following read-only command records its basic proxy settings:
netsh winhttp show proxyWindows browser settings and app-specific proxy settings can differ. Microsoft’s WinHTTP documentation states that resetting the proxy changes it to direct access. That can break connectivity or bypass an organization’s intended route; it is not a harmless certificate repair.
3. Repair the confirmed cause and verify the same scenario
For an inaccessible revocation service, repair the narrowly identified routing or proxy problem. For a missing approved organizational trust chain, have the PKI owner deploy the correct certificates through the managed process. For an expired, revoked, or incorrect server certificate, the server or inspection-proxy owner must repair its configuration. Do not trust a replacement certificate obtained from an unverified prompt.
For organizational Copilot, compare the deployed network policy with Microsoft’s current network requirements. Required endpoints and secure WebSockets matter; TLS inspection can interfere with these connections. Any scoped inspection exception should be a network-security decision, not a user disabling protection across the device.
Retest the original app with certificate validation still enabled. Record what changed and whether the same error and destination remain. A working browser alone does not prove the app is fixed. If unresolved, send sanitized logs, certificate-chain details, proxy context, and reproduction steps to support. Do not delete roots with an error icon, uninstall recent security patches, or invent a CertificateRevocation registry value as a general remedy.