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CO_E_FAILEDTOIMPERSONATE
DCOM server could not impersonate the client
CO_E_FAILEDTOIMPERSONATE is HRESULT 2147549475 (0x80010123) from winerror.h. AllStat describes it as “Unable to impersonate DCOM client.” In the COM IAccessControl, DCOM client identity, trustee translation, token inspection, security descriptor, ACL, or serialization workflow, the code identifies a specific failure boundary and should not be replaced by a generic COM exception.
Telemetry should preserve this result as a separate outcome rather than merging it with unrelated COM or WinRT failures.
Decisive interpretation boundary
Before choosing recovery, verify that the call is authenticated, requested impersonation level permits impersonation, and the server thread still has an active call context. That boundary prevents this result from being misclassified as corruption, network failure, or a reason for an unsafe automatic retry.
Also confirm that all observed objects, tokens, buffers, proxies, metadata files, or ACLs belong to the current operation generation and were not retained from an earlier attempt.
Where it is encountered
- This result can be returned during IAccessControl initialization, access checks, owner/trustee processing, and serialized ACL persistence. Record the interface, method, component version, thread, apartment, process, and correlation ID.
- This result can be returned during server-side DCOM impersonation, client blanket inspection, token and SID lookup.
- It can be returned during security descriptor construction, DACL canonicalization, file-backed policy storage, or legacy NetAccess migration.
The immediate focus for it is server-side client impersonation needed to perform access checks or resource operations under caller identity. Keep it attached to that operation; the same numeric severity outside the owning API does not supply enough context.
Correct handling and recovery
Correct COM security and impersonation levels, perform the operation within the call, or use explicit delegated credentials only through supported policy.
An unchanged retry loop for it can duplicate effects, deepen reentrancy, or hide an invalid lifetime transition.
Difference from nearby HRESULTs
It is a failed impersonation attempt; RPC_E_UNSECURE_CALL says the call was not secure enough to attempt it.
Merging it with the neighboring HRESULT would choose the wrong retry, recreation, authorization, or cleanup path.
Lifetime, retry, and cleanup rules
After it, determine whether the current object, interface pointer, call context, token, stream, metadata reader, asynchronous operation, or access-control instance remains valid. Release only resources owned by the failing attempt, cancel callbacks through their documented mechanism, and avoid double close, double commit, repeated activation, or replay of a non-idempotent remote method.
The retry policy for it should state the trigger, maximum attempts, cancellation owner, and reconciliation step for effects that may have completed elsewhere.
Developer and administrator guidance
When it crosses native, managed, scripting, RPC, or WinRT projection boundaries, preserve the unsigned 32-bit HRESULT. Unit tests for it should assert the code-specific postcondition and resource ownership, not merely that an exception was thrown.
After it, avoid broad permission grants or system-wide resets unless code-specific evidence proves a global configuration problem. Define who owns retry, cancellation, cleanup, policy changes, package repair, and user-facing messaging for it.
Practical scenario
A DCOM file broker tries to impersonate after queuing work beyond method return. It moves the protected open into the active call or captures an approved token safely.
A regression test should reproduce it, assert the raw HRESULT and all relevant outputs, then correct only the decisive condition and verify the intended success or neighboring failure result.
References
- Microsoft: IAccessControl
- Microsoft: IAccessControl::IsAccessAllowed
- Microsoft: AccessCheck
- Microsoft: LookupAccountSidW
- Microsoft: LookupAccountNameW
- Microsoft: access control lists
- Microsoft: canonical ACE order
- Microsoft: HRESULT values
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