CVE-2025-30388: Microsoft Office Buffer Overflow Vulnerability

CVE-2025-30388 Overview

CVE-2025-30388 is a heap-based buffer overflow in the Windows Win32K Graphics (GRFX) component. The flaw allows an unauthorized attacker to execute code locally on affected systems. Successful exploitation requires user interaction but no prior authentication, and impacts confidentiality, integrity, and availability.

Microsoft published the advisory on May 13, 2025. The vulnerability is mapped to CWE-122 (Heap-based Buffer Overflow) and CWE-787 (Out-of-bounds Write). It affects supported releases of Windows 10, Windows 11, Windows Server 2008 through 2025, and Microsoft Office.

Critical Impact
An attacker who triggers the overflow in Win32K - GRFX can run arbitrary code on the target system, leading to full compromise of confidentiality, integrity, and availability.

Affected Products

Microsoft Windows 10 (1507, 1607, 1809, 21H2, 22H2) and Windows 11 (22H2, 23H2, 24H2)
Microsoft Windows Server 2008, 2012, 2016, 2019, 2022, 2022 23H2, and 2025
Microsoft Office and Microsoft Office Long Term Servicing Channel (2021, 2024)

Discovery Timeline

2025-05-13 - CVE-2025-30388 published to NVD
2025-05-19 - Last updated in NVD database

Technical Details for CVE-2025-30388

Vulnerability Analysis

The vulnerability resides in the Win32K Graphics (GRFX) kernel-mode component, which handles graphics device interface operations on Windows. A heap-based buffer overflow occurs when the component writes past the bounds of an allocated heap buffer while processing crafted graphics data. The out-of-bounds write corrupts adjacent kernel heap structures, enabling an attacker to influence kernel execution flow.

Because Win32K runs in kernel mode, a successful overflow grants attacker-controlled code execution at the highest privilege level. The advisory categorizes the issue under both [CWE-122] and [CWE-787], indicating the overflow corrupts heap metadata or adjacent objects through an out-of-bounds write primitive.

The attack requires user interaction, such as opening a malicious file or rendering attacker-supplied graphics content. The EPSS probability is 0.788%, placing it in the 74th percentile of likelihood of exploitation activity.

Root Cause

The root cause is insufficient validation of size or length parameters before writing graphics-related data into a heap-allocated buffer inside the Win32K GRFX subsystem. When the supplied data exceeds the destination buffer, the kernel writes past the allocation boundary and overwrites adjacent heap memory.

Attack Vector

The attack vector is local. An attacker delivers crafted content (for example, a malicious document or graphics resource) to a logged-in user. When the user opens or renders the content, the Win32K GRFX code processes the malformed data and triggers the overflow. The attacker gains code execution in the context of the kernel.

No public proof-of-concept exploit is referenced in the advisory, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2025-30388

Indicators of Compromise

Unexpected kernel-mode crashes (bugchecks) referencing win32k.sys, win32kbase.sys, or win32kfull.sys graphics routines
Suspicious child processes spawned by user applications immediately after opening graphics-rich documents or images
New or modified persistence artifacts created shortly after a Win32K-related crash event

Detection Strategies

Monitor Windows Error Reporting and kernel crash dumps for repeated faults in the Win32K GRFX code path, which can indicate failed exploitation attempts.
Inspect endpoint telemetry for processes loading unusual graphics or font content from untrusted sources prior to a kernel exception.
Correlate document-open events with subsequent privilege transitions or unsigned code execution.

Monitoring Recommendations

Enable kernel crash dump collection on critical endpoints and forward dumps to a centralized analysis pipeline.
Audit Microsoft Office and browser activity for opening files from external email or web sources on unpatched hosts.
Track installation status of the May 2025 Microsoft security updates across all Windows and Office assets.

How to Mitigate CVE-2025-30388

Immediate Actions Required

Apply the Microsoft security update for CVE-2025-30388 to all affected Windows and Office systems as referenced in the Microsoft Security Update CVE-2025-30388 advisory.
Prioritize patching of multi-user systems, workstations handling untrusted documents, and Remote Desktop or VDI hosts where local exploitation is most impactful.
Restrict the ability of standard users to open documents and graphics files originating from external or untrusted sources until patches are deployed.

Patch Information

Microsoft released fixes through the May 2025 security update cycle. Refer to Microsoft Security Update CVE-2025-30388 for the specific KB articles applicable to each Windows and Office release. Install the corresponding cumulative update on every affected SKU listed in the advisory.

Workarounds

No official workaround replaces patching; Microsoft does not list mitigations beyond installing the security update.
Reduce exposure by enforcing Protected View and Attack Surface Reduction rules in Microsoft Office to block content from the internet.
Apply application control policies (Windows Defender Application Control or AppLocker) to limit execution of untrusted binaries that could chain with this local code execution flaw.

bash

# Verify patch installation on Windows hosts
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10

# Enable Office Protected View for files from the internet
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security\ProtectedView" /v DisableInternetFilesInPV /t REG_DWORD /d 0 /f