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RPC_S_UNSUPPORTED_AUTHN_LEVEL
Authentication exists, but the requested RPC protection is unsupported
RPC_S_UNSUPPORTED_AUTHN_LEVEL differs from an unknown numeric authentication level. The level is recognized, but the chosen authentication service, transport, or peer cannot provide it. RPC levels range from no authentication through connect, call, packet, integrity, and privacy protection.
Log the authentication service, principal name, requested level, security QoS, protocol sequence, and whether negotiation selected Kerberos, NTLM, Schannel, or another provider. Do not silently downgrade packet privacy or integrity merely to make the call succeed. Configure a supported service and principal, or explicitly document the lower protection accepted by the application.
What to inspect
- Inspect the negotiated security package rather than only the requested package.
- Verify both peers support the same authentication level.
- Treat an unexpected downgrade as a security configuration defect.
References
- Microsoft: RPC authentication levels
- Microsoft: RPC security essentials
- Microsoft: choosing RPC security QoS
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