CVE-2026-77904 Overview
CVE-2026-77904 is a heap-based buffer overflow [CWE-122] in the Windows Volume Manager Extension Driver. An authenticated local attacker can exploit the flaw to elevate privileges on an affected system. Microsoft assigned the vulnerability a CVSS 3.1 base score of 7.8 with vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, reflecting high impact to confidentiality, integrity, and availability once local access is obtained.
The vulnerability affects a kernel-mode driver, meaning successful exploitation grants SYSTEM-level control over the host. No public exploit code or in-the-wild exploitation has been reported.
Critical Impact
Successful exploitation allows a low-privileged local user to execute code in kernel context and gain full SYSTEM privileges on the affected Windows host.
Affected Products
- Microsoft Windows (Volume Manager Extension Driver component)
- Refer to the Microsoft CVE-2026-77904 Advisory for the authoritative list of affected builds
- Systems running unpatched Windows kernel driver versions
Discovery Timeline
- 2026-09-08 - CVE-2026-77904 published to NVD
- 2026-09-10 - Last updated in NVD database
Technical Details for CVE-2026-77904
Vulnerability Analysis
The flaw resides in the Windows Volume Manager Extension Driver, a kernel-mode component that manages volume operations on Windows storage stacks. A heap-based buffer overflow occurs when the driver writes attacker-influenced data past the bounds of an allocated pool buffer. Because the driver runs in kernel context, corruption of adjacent heap structures can be leveraged to hijack execution flow or overwrite privileged data structures.
Exploitation requires an authenticated local user. The attacker interacts with the driver, likely through DeviceIoControl calls or volume-related APIs, and supplies crafted input that triggers the out-of-bounds write in a pool allocation.
Root Cause
The underlying weakness is classified as [CWE-122] Heap-based Buffer Overflow. The driver fails to correctly validate the size of user-supplied data against the size of a kernel pool buffer before copying. This length mismatch allows adjacent heap metadata or object pointers to be overwritten.
Attack Vector
The attack vector is local. An attacker must first obtain code execution on the target as a standard user, for example through a phishing payload, a compromised service, or an interactive session. From that foothold, the attacker issues crafted requests to the vulnerable driver to trigger the overflow and pivot to SYSTEM. No user interaction is required beyond the attacker's own activity.
Technical exploitation details have not been published. See the Microsoft CVE-2026-77904 Advisory for vendor-provided information.
Detection Methods for CVE-2026-77904
Indicators of Compromise
- Unexpected creation of SYSTEM-level processes originating from standard user sessions or child processes of low-privileged applications.
- Kernel bugchecks or crashes referencing the Volume Manager Extension Driver, which may indicate failed exploitation attempts.
- New or unsigned binaries being executed shortly after suspicious DeviceIoControl activity against volume management devices.
Detection Strategies
- Monitor for anomalous handle opens to volume manager device objects from non-administrative processes.
- Alert on process token elevation events where a child process runs at a higher integrity level than its parent without a legitimate elevation path.
- Correlate Windows Error Reporting (WER) kernel crash telemetry with process execution around the crash window to identify exploitation attempts.
Monitoring Recommendations
- Enable and forward Windows Security, Sysmon, and kernel crash telemetry to a central analytics platform.
- Track patch state across the fleet and alert on Windows hosts missing the fix for CVE-2026-77904.
- Baseline normal driver interaction patterns so unusual IOCTL activity against storage drivers surfaces as an anomaly.
How to Mitigate CVE-2026-77904
Immediate Actions Required
- Apply the Microsoft security update for CVE-2026-77904 as documented in the Microsoft CVE-2026-77904 Advisory.
- Prioritize patching on multi-user systems, virtual desktop infrastructure, and any host where untrusted users can execute code.
- Audit local administrator group membership and remove unnecessary standing privileges to reduce lateral impact.
Patch Information
Microsoft has released a security update addressing the heap-based buffer overflow in the Volume Manager Extension Driver. Consult the Microsoft CVE-2026-77904 Advisory for the specific KB numbers and build versions applicable to each supported Windows release. Deploy the update through Windows Update, WSUS, Microsoft Intune, or your standard patch management workflow.
Workarounds
- No official vendor workaround has been published. Patching is the recommended remediation.
- Restrict interactive and remote logon rights so only trusted accounts can execute code locally on sensitive systems.
- Enforce application allowlisting to limit the ability of unauthorized binaries to interact with kernel drivers.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.