CVE-2026-54991 Overview
CVE-2026-54991 is a race condition vulnerability in the Windows USB Print Driver. The flaw stems from concurrent execution using a shared resource with improper synchronization. An authorized local attacker can exploit the timing window to elevate privileges on affected systems. Microsoft has assigned the vulnerability a high severity rating.
The vulnerability affects multiple current Windows client and server platforms, including Windows 11 24H2, 25H2, 26H1, and Windows Server 2025. Successful exploitation grants attackers elevated privileges, enabling further post-compromise activity such as credential theft, persistence, and lateral movement.
Critical Impact
A local authorized attacker who wins the race condition in the Windows USB Print Driver can escalate to higher privileges, compromising confidentiality, integrity, and availability of the host.
Affected Products
- Microsoft Windows 11 24H2 (ARM64, x64)
- Microsoft Windows 11 25H2 (ARM64, x64)
- Microsoft Windows 11 26H1 (ARM64, x64)
- Microsoft Windows Server 2025
Discovery Timeline
- 2026-07-14 - CVE-2026-54991 published to NVD
- 2026-07-20 - Last updated in NVD database
Technical Details for CVE-2026-54991
Vulnerability Analysis
The vulnerability is a race condition (CWE-362-class flaw) within the Windows USB Print Driver. Multiple threads access a shared resource without proper synchronization primitives. An attacker who can time operations precisely can manipulate driver state between validation and use.
The NVD entry also lists CWE-125 (Out-of-Bounds Read), suggesting the race condition can lead the driver to read memory outside intended boundaries when the shared resource is modified mid-operation. Exploiting the race requires local access and low privileges, but the attack complexity is high due to the timing requirements. Successful exploitation impacts confidentiality, integrity, and availability at the operating system level.
Root Cause
The root cause is improper synchronization of concurrent operations on a shared resource inside the USB Print Driver. When two code paths access the same driver object without adequate locking, one thread can modify data structures while another consumes them. This introduces a time-of-check to time-of-use (TOCTOU) condition that can be steered toward memory corruption or logic errors executing at kernel privilege.
Attack Vector
Exploitation requires an authenticated local user on the target host. The attacker must trigger driver code paths concurrently and win a timing window to influence how the driver processes USB print operations. Because the driver runs with elevated privileges, a successful race allows the attacker to escalate from a standard user context to a higher privilege level. No user interaction is required beyond executing the attacker-controlled process. Detailed exploitation mechanics are documented in the Microsoft CVE-2026-54991 Advisory.
Detection Methods for CVE-2026-54991
Indicators of Compromise
- Unexpected child processes spawned by services running under SYSTEM after USB print driver activity.
- Anomalous loading or repeated loading of USB print driver components such as usbprint.sys by non-print workflows.
- Crash dumps or Event Log entries referencing faults in the USB Print Driver stack under System provider.
Detection Strategies
- Monitor for local privilege escalation patterns: token manipulation, integrity-level changes, and new privileged process trees originating from unprivileged users.
- Alert on rapid, repeated open/close or IOCTL activity targeting USB print device objects, which is characteristic of race condition exploitation attempts.
- Correlate driver crashes (WerFault.exe, bugcheck events) with prior process activity from standard user sessions.
Monitoring Recommendations
- Ingest Windows kernel and driver telemetry into a centralized analytics platform to identify timing-based anomalies.
- Track privilege changes on user tokens and flag processes that acquire SeDebugPrivilege or SYSTEM context without expected parentage.
- Baseline normal USB print driver usage per host and alert on deviations, particularly on servers where interactive print activity is rare.
How to Mitigate CVE-2026-54991
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft CVE-2026-54991 Advisory to all affected Windows 11 and Windows Server 2025 hosts.
- Prioritize patching of multi-user systems, jump hosts, and terminal servers where local users could stage the attack.
- Restrict local logon rights on servers and privileged workstations to reduce the population of accounts that meet the attacker prerequisites.
Patch Information
Microsoft has published a security update for CVE-2026-54991 as part of its Update Guide. Administrators should deploy the corresponding cumulative update for Windows 11 24H2, 25H2, 26H1, and Windows Server 2025 through Windows Update, WSUS, or their preferred patch management tooling. Refer to the Microsoft CVE-2026-54991 Advisory for build-specific KB numbers.
Workarounds
- Where patching is delayed, disable or restrict the USB Print Driver on systems that do not require USB printing functionality.
- Enforce least-privilege policies and remove unnecessary local accounts from hosts exposed to untrusted users.
- Apply Windows Defender Application Control (WDAC) or AppLocker policies to prevent execution of untrusted binaries that could stage the race condition exploit.
# Configuration example: disable the USB Print class driver service until patched
sc.exe config usbprint start= disabled
sc.exe stop usbprint
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
