LSI (Agere, Lucent) Fax Modem support disabled in Windows 10/11 cumulative update
In October 2025, a cumulative update for Windows 11 and 10 was released. It removed a third-party Lucent (Agere) Modem driver. This was due to an Elevation of Privilege Vulnerability. This driver ships natively with supported Windows operating systems. The driver file ltmdm64.sys (x64) was used for several types of soft modems using the Lucent/Agere chipset.
In January 2026, a cumulative update for Windows 11 (KB5073455) and Windows 10 (KB5073724) removed additional modem drivers: agrsm64.sys (x64), agrsm.sys (x86), smserl64.sys (x64) and smserial.sys (x86). This includes Agere, LSI (Lucent) and Motorola type modems.
Fax modem hardware dependent on these drivers will no longer work on Windows. Microsoft recommends removing any existing dependencies on this hardware.
By default, the driver files are stored in the Windows\System32\Driver folder, ensuring it’s accessible even if the hardware isn’t installed.
Affected model names of LSI/Agere Modems (As of January 23, 2026)
The following models use the Ltmdm64.sys (x64) driver file.
L56xM+S [Mars-2] WinModem 56k
LT Winmodem or LSI SoftModem
Winmodem 56K
F-1156IV WinModem (V90, 56KFlex)
Vendor ID : 11C1 (Lucent)
Device IDs : DEV_0440 , DEV_0441, DEV_0442, DEV_0443, DEV_0444, DEV_0445, DEV_0446, DEV_0447, DEV_0448, DEV_0449, DEV_044A, DEV_044B, DEV_044C, DEV_044D, DEV_044E, DEV_0450, DEV_0451, DEV_0452, DEV_0453, DEV_0454, DEV_0455, DEV_0456, DEV_0457, DEV_0458, DEV_0459, DEV_045A, DEV_045B, DEV_045C, DEV_044E&SUBSYS_044E1235, DEV_044C&SUBSYS_044C11C1
The following fax modem models use agrsm64.sys (x64), agrsm.sys (x86), smserl64.sys (x64) and smserial.sys (x86)
Agere Systems AC’97 Modem
Motorola SM56 Modem
HIRO H50113 (USB LSI software modem)
U.S. Robotics USR5638 (internal PCI Express)
U.S. Robotics USR5639 (USB LSI software modem)
U.S. Robotics USR5670 (internal PCI Express)
StarTech USB56KEM3
TOSHIBA Software Modem
Agere Systems PCI Soft Modem
Samsung LT56ADW Modem
SENS LT56ADW Modem
Agere Systems HDA Modem
Agere Systems PCI-SV92PP Soft Modem
Agere Systems USB 2.0 Soft Modem
AGERE PCI-SV92EX Soft Modem
Lucent External Voice Modem
Actiontec V.90 PCI Modem
Actiontec 56K PCI Modem
More information
https://nvd.nist.gov/vuln/detail/CVE-2025-24052
Questions and Answers
Q. What brand of modems are affected?
A. Motorola, Agere, Lucent, and later LSI licensed their chipsets to a variety of modem manufacturers. Brands that used the Lucent chipset included U.S. Robotics, Startech.com, Hiro Inc., InterTAN, and many others. Most of these models have since been discontinued by their manufacturers. The Motorola chipset was also common for many older (1997 and later), internal fax modems.
Q. I use a Conexant based fax modem; will I be affected with this vulnerability?
A. The Conexant modem will continue to work, it is not affected by this vulnerability.
Q. What privileges could be gained by an attacker who successfully exploited the vulnerability?
A. An attacker who successfully exploited this vulnerability could gain administrator privileges.
Q. Is the vulnerability only exploitable if the Lucent/Agere Modem or Motorola Modem is actively being used on the computer?
A. No. All supported versions of Windows are vulnerable and could be exploited from this issue.
Q. Does this specific vulnerability give an attacker remote access to my machine?
A. No. It is a local vulnerability, but once the machine is compromised an attacker could install malicious software including remote access.
Q. How do I protect my system?
A. Install the latest cumulative updates for Windows. If you use one of the modems listed below, it will be disabled and no longer working in Windows. We recommend you replace it.
Q. I need to replace my modem. Which one should I buy?
A. There are a lot of modems on the market, but they’re not all created equal. Some suffer from poor build quality, while others have software drivers that just don’t play nice. Even with the default Windows driver, certain features your software needs—like Caller ID or telephone audio playback—probably won’t work. In some situations, you might even be forced to install a driver with Memory Integrity turned off in Windows 11. None of the current fax voice modems we offer have these problems. If you do run into a problem, we’re there to help you. Check our shop
Reverting changes to support LT WinModem
To revert the changes. you can remove (uninstall) the January 2026 update, and/or October 2025 update from Windows. This is not recommended.
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