Windows 10 Security Alert: Why Modern Apps Are Being Blocked & How to Fix It

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This article addresses a specific scenario encountered by some users on Windows 10, where legitimate modern applications (often referred to as Universal Windows Platform or UWP apps) are unexpectedly flagged and blocked by third-party security software. We will delve into the underlying technical reason for this behavior and provide a practical workaround to resolve the issue, allowing affected applications to run normally.

This issue has been noted on several versions of Windows 10, including version 1607, version 1809, and version 1903. Users running these specific builds may encounter this problem with various modern applications obtained from the Microsoft Store or deployed via other standard UWP distribution methods. Understanding the cause is key to implementing the correct solution.

Symptoms: Applications Unexpectedly Blocked¶

Users encountering this issue will typically observe that when they attempt to launch a modern application, the application fails to start. Instead of the app window appearing, they may receive a notification or alert from their installed security software. This alert will usually indicate that the application execution has been prevented because the software considers it a potential threat, suspicious, or unauthorized.

Common examples of affected applications include built-in Windows apps or standard Microsoft Store apps, such as Microsoft.MSN.Money.exe (the Money app) or Microsoft.Photos.exe (the Photos app). The specific notification message will vary depending on the security product in use (e.g., antivirus, endpoint protection platform). Users might see messages referencing unsigned files, unknown executables, or policy violations related to application control. The core symptom remains consistent: the legitimate modern app is prevented from running by the security software.

This blocking behavior can be frustrating as it prevents access to necessary or frequently used applications. The user might be left wondering why a seemingly harmless, built-in, or store-downloaded app is being treated as a threat by their security solution. Identifying which security software is causing the block is the first step in troubleshooting, often requiring checking the security product’s notification history or logs.

Cause: Signature Discrepancy¶

The root cause of this issue lies in a technical detail regarding how modern applications are packaged and signed on Windows 10 compared to how some security software evaluates executable files. Modern applications are distributed as packages (using formats like .appx or .msix). These packages are digitally signed by Microsoft or the application developer to ensure their authenticity and integrity. This package signature confirms that the app originates from a trusted source (like the Microsoft Store) and has not been tampered with since it was signed.

However, the individual executable files (.exe, .dll, etc.) contained within these digitally signed packages are often not individually digitally signed. While the package itself bears a valid signature attesting to the integrity of its contents as a whole, the files extracted or accessed from within the package during runtime lack their own separate digital signatures. Traditional security software, especially older versions or those employing stricter heuristic analysis or application control policies, might inspect individual files as they are accessed or executed. When such software encounters an executable file without an individual digital signature, even if it originated from a validly signed package, it may flag it as suspicious or untrusted.

This discrepancy – a validly catalog-signed package containing files that are not individually signed – is interpreted by certain security products as a potential risk. Security software often uses digital signatures as a primary method for verifying the trustworthiness of executables. An unsigned executable file, regardless of its origin from a signed package, might trigger alerts based on policies that require all executables to have individual signatures or based on heuristics that associate unsigned code with potentially malicious activity. Essentially, the security software is focusing on the individual file signature rather than the package’s catalog signature, leading to a false positive for legitimate modern applications.

Understanding Digital Signatures and App Packaging¶

To further clarify the cause, it’s helpful to understand the signing process.
1. Individual File Signing: This involves embedding a digital signature directly into the executable or library file itself (.exe, .dll). When the operating system or security software checks the file, it reads the signature directly from the file header or structure. This is common for traditional Win32 applications.
2. Catalog Signing: This method involves creating a catalog file (.cat) that contains cryptographic hashes of multiple files. This catalog file is then digitally signed. When the operating system or security software needs to verify the integrity of the files listed in the catalog, it computes the hash of the individual file and compares it to the hash stored in the signed catalog file. If the hashes match and the catalog file’s signature is valid and trusted, the individual files are considered validated through association. Modern app packages often use catalog signing or a similar mechanism where the package itself is signed, and the package manifest lists the contents and their hashes, effectively serving a similar purpose to a signed catalog for verifying package integrity.

The issue arises because some security products are primarily designed or configured to check for individual file signatures. When a modern app’s executable (like Microsoft.Photos.exe) is accessed from its package, the security software might perform a signature check on that specific .exe file. Finding no embedded signature, despite the fact that the .exe’s integrity is verified by the signed package it came from, the security software triggers an alert and blocks execution. This behavior highlights a potential mismatch in how some security solutions interpret the signing model used by modern Windows applications.

Security Software Perspective¶

Security software operates under the principle of minimizing risk. While modern app packages provide a robust security model through package signing and isolation, some security products employ layers of defense that include scrutinizing individual processes and files.
* Heuristics: Detecting suspicious patterns or characteristics. An unsigned executable might be one such characteristic flagged by heuristics, especially if combined with other factors (though in this case, for legitimate apps, it’s likely the lack of signature is the primary trigger).
* Application Control Policies: Strict policies might mandate that all executed code must be digitally signed by a trusted vendor. The absence of an individual signature would violate such a policy.
* Signature Databases: Some security solutions rely on databases of known trusted or malicious file signatures. While they might recognize Microsoft’s package signing certificate, they may not inherently trust every file originating from such a package unless those files themselves are individually signed or specifically whitelisted.

This particular issue seems to stem from the security software’s focus on the individual file signature verification mechanism, which is different from the package-level verification mechanism used by modern apps and the operating system.

Workaround: Add Applications to Allow Lists¶

The most effective and direct way to resolve this issue, as identified by the original source of this information, is to configure your security software to explicitly allow the affected modern applications to run. This process involves adding the specific application executable or its package to the “allow list,” “exclusion list,” or “trusted programs” list within your security software’s settings.

Here’s a general approach to implementing this workaround:

1. Identify the Security Software: Determine which security product is causing the block. This is usually indicated by the alert message that appears when you try to launch the app.
2. Locate the Application Executable: You need the exact path or name of the executable file that is being blocked. For modern apps, these are typically located in protected system folders, often within C:\Program Files\WindowsApps\. Finding the exact path can sometimes be tricky due to folder permissions, but the executable name (e.g., Microsoft.Photos.exe, Microsoft.MSN.Money.exe) is usually what the security software’s alert will mention. You might need to enable viewing hidden files and folders, and potentially take ownership of the WindowsApps folder (exercise caution when modifying permissions in system folders). A safer approach might be to look for the application name or package name in the security software’s logs or alerts, which might provide the necessary identifier.
3. Access Security Software Settings: Open the user interface of your security software (antivirus, endpoint protection, etc.).
4. Navigate to Exclusions/Allow Lists: Find the section related to exclusions, exceptions, trusted files, or application control. The exact naming varies widely between different security products (e.g., “Exclusions,” “Allowed Apps,” “Threats and Exclusions,” “Whitelisting”).
5. Add the Application: Add the identified application executable file (using its full path) or the application package name to the allow list. Some security software might allow adding by process name, file hash, or even certificate (though adding by file path or name is most common for this issue). You might need to add the specific .exe file or potentially the entire application package folder, depending on the software’s capabilities.
6. Save Changes: Apply or save the changes within your security software.

Once the application is added to the allow list, the security software should no longer interfere with its execution, and the modern app should launch correctly.

Potential Risks and Considerations¶

While this workaround directly addresses the blocking issue, it’s crucial to understand the implications:
* Bypassing Security Checks: Adding an application to an allow list tells your security software to ignore it for certain checks. While this is necessary for legitimate apps in this scenario, it means that if the allowed app were ever to become compromised or infected in a way that changes its executable (which is difficult with signed packages, but not theoretically impossible), the security software might not detect it.
* Specificity: Be as specific as possible when adding exceptions. Ideally, add only the specific executable file that is being blocked. Avoid adding entire folders or overly broad exceptions unless necessary, as this could potentially weaken your security posture.
* Updates: If the modern application updates, its executable path or internal structure might change. In some cases, you might need to update the exclusion in your security software after an app update.
* Security Software Updates: Keep your security software updated. Future versions of your security product might be updated to better handle the modern app signing model, potentially resolving the issue without requiring manual exclusions. Check for updates from your security vendor.

This workaround should be considered a temporary measure if your security vendor releases an update addressing this specific false positive behavior. However, for the Windows 10 versions mentioned and with certain security software, this may remain the necessary step to ensure proper functionality of modern apps.

Example: Finding App Path (Illustrative)¶

Locating the executable for a modern app can be challenging. For example, the Photos app might be located in a path similar to:
C:\Program Files\WindowsApps\Microsoft.Windows.Photos_2022.31100.10004.0_x64__8wekyb3d8bbwe\Microsoft.Photos.exe

Note that the version number (2022.31100.10004.0) and the build string (8wekyb3d8bbwe) in the folder name will vary based on the app version and your specific installation. This is why adding an exclusion by process name (Microsoft.Photos.exe) or by allowing the specific package folder (Microsoft.Windows.Photos_...) might be more reliable than using a full, static file path, depending on your security software’s capabilities. Security software logs are the best place to find the exact path or process name being blocked.

Broader Context: Windows Security and Application Trust¶

This specific issue highlights the complex interplay between the operating system’s evolving security models (like UWP apps and packaging) and external security software. Windows 10 implements various security features for modern apps, including app isolation (running in a sandbox) and mandatory package signing. These features are designed to enhance security by limiting an app’s access to system resources and verifying its origin and integrity.

However, third-party security solutions often employ their own detection engines, heuristics, and policy enforcement mechanisms that operate alongside or integrate with Windows’ built-in security. Differences in how these systems interpret specific technical details, like the absence of individual file signatures within a catalog-signed package, can lead to compatibility issues or false positives like the one discussed.

Microsoft provides developers with tools and guidelines for packaging and signing modern apps. The catalog signing or package signing approach is a standard practice for UWP applications distributed through the Microsoft Store. The expectation is that the operating system and compatible security software will trust applications based on the validity of the package signature. When security software deviates from this trust model by requiring individual file signatures for components within a valid package, it creates the conflict.

This scenario is not uncommon in the world of cybersecurity, where the dynamic threat landscape and the continuous evolution of software and operating systems require security vendors to constantly update their detection methods. False positives, while inconvenient, are sometimes an unavoidable byproduct of aggressive detection techniques aimed at preventing new or unknown threats. In this case, the behavior seems to be a misinterpretation of a legitimate application packaging method by certain security software configurations.

Troubleshooting Steps¶

If you encounter this issue, here are steps to diagnose and apply the workaround:

1. Confirm the Block: Attempt to launch the modern app. Observe if any security alerts pop up or if the application simply fails to start without error.
2. Identify Blocking Software: Check your system tray for icons of running security software (antivirus, EDR, etc.). Open the main window of each likely candidate and look for recent alerts, quarantine lists, or event logs. The security software’s logs should explicitly state that it blocked an application and usually provide the name and path of the blocked executable.
3. Note Block Details: Write down the exact application name, path, and the reason given by the security software for the block (e.g., “unsigned file,” “policy violation,” specific threat name if misidentified).
4. Consult Security Software Documentation: Refer to the help files or online documentation for your specific security software to find instructions on how to add files or applications to its exclusion or allow list. The process varies significantly between vendors (e.g., McAfee, Symantec, CrowdStrike, Windows Defender, etc.).
5. Implement the Workaround: Follow the steps outlined in the “Workaround” section using the details gathered in step 3 and the instructions from step 4. Start by trying to add the specific executable file path. If that doesn’t work, check if your security software allows adding by process name or package name, or if adding the entire application package folder is an option.
6. Test the Application: After adding the exclusion, try launching the modern app again. It should now start without being blocked.
7. Contact Security Vendor Support (Optional but Recommended): If adding the exclusion is difficult or if you are concerned about the security implications, consider contacting the technical support for your security software vendor. Inform them about the false positive with the specific modern application on your Windows 10 version. Providing them with logs and details can help them improve their detection logic in future updates, potentially resolving the issue for other users.

Remember to keep both your Windows operating system and your security software updated to receive the latest security patches and detection improvements.

Conclusion¶

The blocking of modern applications by security software on certain Windows 10 versions is primarily caused by some security products incorrectly flagging legitimate, unsigned executable files contained within validly signed app packages. While the package itself is signed, the individual components might not be, leading to a false positive based on how the security software performs its checks.

The recommended workaround involves configuring your security software to add the affected modern applications to its allow list. This tells the security software to trust and permit the execution of these specific applications, resolving the blocking issue. While implementing this workaround, it is important to add exclusions carefully and specifically to avoid unnecessarily reducing your system’s security protection. Staying informed about your security software’s settings and keeping it updated are crucial steps in managing such compatibility issues effectively.

Have you encountered this issue with your modern apps on Windows 10? Which security software were you using? Share your experiences or ask questions in the comments below!