CVE-2025-49697: Microsoft 365 Apps Buffer Overflow Flaw

CVE-2025-49697 Overview

CVE-2025-49697 is a heap-based buffer overflow vulnerability in Microsoft Office that allows an unauthorized attacker to execute code locally. The flaw, tracked under CWE-122, affects multiple Office editions including Microsoft 365 Apps, Office 2016, Office 2019, Office LTSC 2021, Office LTSC 2024, and Office Online Server. Microsoft published the advisory on July 8, 2025, and the issue carries a CVSS 3.1 base score of 8.4. Successful exploitation results in full compromise of confidentiality, integrity, and availability on the targeted system.

Critical Impact

Attackers can achieve arbitrary code execution under the context of the user running Microsoft Office, enabling malware deployment, credential theft, and lateral movement.

Affected Products

• Microsoft 365 Apps (Enterprise, x86 and x64)
• Microsoft Office 2016 and Office 2019 (x86 and x64)
• Microsoft Office LTSC 2021 and LTSC 2024 (Windows and macOS)
• Microsoft Office Online Server

Discovery Timeline

• 2025-07-08 - CVE-2025-49697 published to NVD and Microsoft Security Response Center advisory released
• 2025-07-15 - Last updated in NVD database

Technical Details for CVE-2025-49697

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow (CWE-122) within Microsoft Office document parsing routines. When Office processes a specially crafted document, it writes data beyond the bounds of a heap-allocated buffer. This corruption allows an attacker to overwrite adjacent heap structures, including object metadata and function pointers used by Office components.

By controlling the layout of the heap before triggering the overflow, an attacker can hijack control flow and execute arbitrary code in the security context of the user opening the document. The attack does not require elevated privileges or user interaction beyond opening the malicious file, which aligns with common phishing-driven delivery patterns for Office exploits.

Root Cause

The root cause is improper validation of size or length fields during the parsing of attacker-controlled document content. Office allocates a heap buffer based on one length value but copies data using another, producing an out-of-bounds write on the heap. Microsoft's advisory does not disclose the specific file format or parser involved.

Attack Vector

The attack vector is local: the attacker must deliver a crafted Office document, typically via email attachment, file share, or web download, to the victim. Once the document is opened in a vulnerable Office build, the parser triggers the heap overflow and the embedded payload executes. The Preview Pane is commonly leveraged for similar Office vulnerabilities, lowering the interaction threshold further.

No public proof-of-concept exploit code is currently available, and the vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog. The EPSS probability stands at 0.615% as of the latest scoring data, indicating moderate predicted exploitation activity over the next 30 days.

Detection Methods for CVE-2025-49697

Indicators of Compromise

• Unexpected child processes spawned by winword.exe, excel.exe, powerpnt.exe, or outlook.exe, particularly cmd.exe, powershell.exe, rundll32.exe, or mshta.exe.
• Office processes writing executables, scripts, or DLLs to user-writable locations such as %TEMP%, %APPDATA%, or %PUBLIC%.
• Crash dumps or Windows Error Reporting events referencing heap corruption inside Office binaries.
• Inbound emails delivering Office documents from untrusted senders, especially when paired with social-engineering lures.

Detection Strategies

• Hunt for anomalous parent-child process relationships originating from Office applications across endpoint telemetry.
• Monitor for module loads of LOLBins or unusual DLLs into Office processes following document open events.
• Correlate Office application crashes with subsequent process creation or network connection events to surface exploitation attempts.

Monitoring Recommendations

• Ingest Office, Sysmon, and EDR process telemetry into a centralized analytics platform for behavioral correlation.
• Alert on outbound network connections initiated directly by Office processes to non-Microsoft destinations.
• Track patch deployment status for all Office SKUs listed in the Microsoft advisory to identify unpatched endpoints.

How to Mitigate CVE-2025-49697

Immediate Actions Required

• Apply the July 2025 security updates for all affected Microsoft Office and Microsoft 365 Apps channels as listed in the Microsoft Security Update CVE-2025-49697 advisory.
• Inventory endpoints running Office 2016, 2019, LTSC 2021, LTSC 2024, and Office Online Server, and prioritize patching for internet-exposed and high-value users.
• Restrict execution of macros and active content from untrusted sources using Group Policy or Intune configuration.

Patch Information

Microsoft has released security updates addressing CVE-2025-49697 through the standard Office and Microsoft 365 Apps update channels. Click-to-Run installations should receive the fix automatically once update channels are enabled. Refer to the Microsoft Security Update CVE-2025-49697 advisory for build numbers and KB articles per product.

Workarounds

• Enable Protected View and Application Guard for Office to isolate documents from untrusted sources.
• Disable the Outlook Preview Pane to reduce automatic rendering of attacker-supplied attachments.
• Block inbound Office document attachments from external senders at the email gateway, or detonate them in a sandbox prior to delivery.
• Apply Attack Surface Reduction (ASR) rules that block Office applications from creating child processes and from injecting code into other processes.

# Enable ASR rules via PowerShell to limit Office exploitation impact
Set-MpPreference -AttackSurfaceReductionRules_Ids `
  D4F940AB-401B-4EFC-AADC-AD5F3C50688A, `
  3B576869-A4EC-4529-8536-B80A7769E899, `
  75668C1F-73B5-4CF0-BB93-3ECF5CB7CC84 `
  -AttackSurfaceReductionRules_Actions Enabled,Enabled,Enabled