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Windows 11 KB5074109: USB/Dial-up Analog Modems Stop Working (Legacy Driver Components Blocked)

Contents

Overview

After installing Microsoft’s Windows 11 security update KB5074109 (January 13, 2026; OS Builds 26200.7623 / 26100.7623), USB/dial-up style analog modems may stop functioning. This occurs due to an OS-level compatibility/security change where Windows intentionally removes/blocks specific legacy modem driver components for security reasons (security context includes vulnerabilities such as CVE-2024-55414, e.g., involving SmSerl64.sys).

This is not a GFI FaxMaker defect. Impact depends on whether the modem’s driver stack relies on the legacy driver files removed/blocked by KB5074109.

Solution

1) Identify whether your modem is impacted (driver-stack acceptance test)

On the Windows 11 FaxMaker server (or a Windows 11 test machine with KB5074109 installed):

  1. Open Device Manager.
  2. Expand Modems.
  3. Right-click the modem → Properties.
  4. Go to Driver → Driver Details.
  5. If you see any of the following files listed, the modem is impacted by KB5074109:
    • agrsm64.sys / agrsm.sys
    • smserl64.sys / smserial.sys

2) Choose a mitigation / resolution option

Option A (short-term, Windows-level workaround): Uninstall KB5074109 (if policy allows)

  1. Uninstall KB5074109 from Windows Update history / installed updates.
  2. Reboot the server if prompted.
  3. Pause/deferral of updates may be required until a long-term plan is implemented.

Notes:

  • This restores the removed in-box modem components only while the update remains uninstalled.
  • Ensure your security policy/compliance requirements allow removing or deferring the update.

Option B (preferred long-term mitigation): Replace the modem with a device that does not rely on the removed legacy files

Compatibility is determined by the driver stack (the driver file dependencies), not the modem brand/model name alone. Use the following selection rule:

  1. Prefer devices with a current, vendor-supplied, signed Windows 11 driver.
  2. Avoid solutions that rely on the removed legacy driver files:
    • agrsm64.sys / agrsm.sys
    • smserl64.sys / smserial.sys
  3. Validate before committing:
    • On Windows 11 with KB5074109 installed, connect/install the candidate device.
    • Repeat Device Manager → Modems → Properties → Driver → Driver Details.
    • Confirm it does not list agrsm*.sys or smserl64.sys/smserial.sys.

Option C (most durable for reliability): Move to a supported Fax-over-IP (FoIP) implementation

If your environment can support it, a supported FoIP implementation reduces dependency on Windows legacy modem driver components and is less likely to be disrupted by future OS security hardening.

Validation (Post-change Checks)

After applying Option A, B, or C:

  1. Confirm the device is present and healthy in Device Manager (no driver warnings).
  2. Perform an end-to-end FaxMaker send/receive test using a known-good fax destination/test line.
  3. If using Option B, re-check Driver Details to ensure the legacy file dependencies are not present.

Frequently Asked Questions

1. How do I know if this is the same KB5074109 issue?
If the modem stopped working after installing Windows 11 update KB5074109, check Device Manager → Modems → Properties → Driver → Driver Details. If you see agrsm64.sys/agrsm.sys or smserl64.sys/smserial.sys, the modem is impacted by the KB5074109 legacy-driver removal/blocking.
2. What is the exact error message for this problem?
No specific Windows/FaxMaker error text or error code was provided in the report. The identifying indicator is the presence of the legacy driver files in Driver Details and the timing of failure after KB5074109 installation.
3. Can you recommend a specific “known compatible after KB5074109” USB modem model?
Compatibility depends on the device’s driver stack (the specific driver files it uses), not the brand/model name alone. Use the acceptance test: install the device on Windows 11 with KB5074109 and verify Driver Details does not reference agrsm*.sys or smserl64.sys/smserial.sys.
4. Is this a GFI FaxMaker defect?
No. This is an OS-level change in Windows 11 introduced by KB5074109 to remove/block legacy modem driver components for security reasons (security context includes CVE-2024-55414).
5. What should I do if uninstalling KB5074109 is not allowed?
Move to hardware/software that uses a current vendor-supplied, signed Windows 11 driver that does not depend on the removed legacy files, or migrate to a supported FoIP implementation to avoid reliance on legacy modem driver components.
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  1. Priyanka Bhotika

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