Fix for Server Challenge Token Security Incident

[stefong99]

Description

This change makes a fix for CVE-2025-47158

Incident 31000000381506 : [MSRC] [98867] - ElevationOfPrivilege - Local Privilege Escalation that results in Arbitrary File Read in Azure File Sync Agent on Arc enabled Windows server

Mandatory Checklist

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Pull Request Overview

This PR addresses CVE-2025-47158 by strengthening how the server challenge token’s secret file path is parsed and validated.

• Renamed and clarified the header variable and improved its parsing
• Centralized path normalization and validation in a new IsSecretFilePathValid helper
• Updated error handling to use a consistent error resource

Comments suppressed due to low confidence (3)

src/StorageSync/StorageSync/Interop/ManagedIdentity/ServerManagedIdentityUtils.cs:275

• [nitpick] The variable name wwwHeader is ambiguous. Consider renaming it to something more descriptive like authenticateHeaderValue or challengeHeaderValue to improve readability.

                    var wwwHeader = authenticateHeaderValues.FirstOrDefault();

src/StorageSync/StorageSync/Interop/ManagedIdentity/ServerManagedIdentityUtils.cs:344

• The new IsSecretFilePathValid method contains critical security logic but lacks dedicated unit tests. Please add tests covering valid paths, invalid paths, edge cases, and path traversal attempts.

        private static bool IsSecretFilePathValid(string secretFilePath)

src/StorageSync/StorageSync/Interop/ManagedIdentity/ServerManagedIdentityUtils.cs:296

• [nitpick] Reusing the same error message for both a missing secret file and an invalid path may be confusing. Consider using distinct error codes or messages to differentiate missing file vs invalid path scenarios.

                            StorageSyncResources.AgentMI_InvalidSecretFileError,

[YanaXu]

/azp run azure-powershell - security-tools

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Azure Pipelines successfully started running 1 pipeline(s).

[YanaXu]

Please provide the test result before and after this change. Thanks!