CVE-2025-27481: Windows 10 1507 Buffer Overflow Vulnerability

CVE-2025-27481 Overview

CVE-2025-27481 is a stack-based buffer overflow vulnerability in the Windows Telephony Service (TAPI) that enables an unauthorized attacker to execute arbitrary code over a network. This vulnerability affects a wide range of Microsoft Windows operating systems, including both client and server editions, making it a significant threat to enterprise environments.

The Windows Telephony Service provides telephony API (TAPI) functionality for applications that need to communicate with telephony devices. Due to improper bounds checking when processing network requests, an attacker can craft malicious input that overflows a stack buffer, potentially leading to remote code execution.

Critical Impact

Successful exploitation allows an unauthorized attacker to execute arbitrary code remotely, potentially gaining complete control over affected Windows systems without requiring authentication.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2)
• Microsoft Windows 11 (versions 22H2, 23H2, 24H2)
• Microsoft Windows Server 2008 SP2, 2008 R2 SP1, 2012, 2012 R2, 2016, 2019, 2022, 2022 23H2, 2025

Discovery Timeline

• 2025-04-08 - CVE-2025-27481 published to NVD
• 2025-07-08 - Last updated in NVD database

Technical Details for CVE-2025-27481

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow). The Windows Telephony Service fails to properly validate the length of input data before copying it into a fixed-size stack buffer. When an attacker sends a specially crafted request to the service over the network, the excessive data overwrites adjacent memory on the stack, including critical control structures such as return addresses and saved frame pointers.

The attack can be initiated remotely across the network but does require some form of user interaction to trigger the vulnerable code path. Once exploited, the attacker can achieve complete compromise of the affected system with the same privileges as the Telephony Service, which typically runs with elevated permissions.

Root Cause

The root cause of CVE-2025-27481 lies in insufficient bounds checking within the Windows Telephony Service when handling incoming data. The service allocates a fixed-size buffer on the stack and copies user-supplied input without properly validating that the input length does not exceed the buffer capacity. This classic stack-based buffer overflow pattern allows attackers to corrupt stack memory and redirect program execution flow.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An attacker can send malicious requests to the Windows Telephony Service from across the network. The vulnerability requires user interaction, suggesting that exploitation may involve convincing a user to interact with a malicious telephony application or service request.

The exploitation flow involves sending an oversized payload that exceeds the allocated stack buffer, overwriting the saved return address with an attacker-controlled value. When the vulnerable function returns, execution transfers to the attacker's shellcode or ROP gadgets, achieving arbitrary code execution.

Detection Methods for CVE-2025-27481

Indicators of Compromise

• Unusual network traffic targeting TAPI-related ports or services
• Crash dumps or error logs from tapisrv.dll or the Telephony Service (TapiSrv)
• Unexpected processes spawned as children of the Telephony Service
• Evidence of stack buffer overflow exploitation in Windows Event Logs

Detection Strategies

• Monitor Windows Event Logs for Application Error events (Event ID 1000) involving the Telephony Service or tapisrv.dll
• Deploy network intrusion detection signatures to identify malformed TAPI requests with abnormally large data fields
• Enable Windows Defender Exploit Guard to detect and block stack buffer overflow attempts
• Implement memory protection monitoring for stack canary violations in critical services

Monitoring Recommendations

• Configure alerting on unexpected restarts or crashes of the Telephony Service
• Monitor network connections to systems with TAPI enabled for anomalous connection patterns
• Deploy endpoint detection and response (EDR) solutions to identify post-exploitation behaviors such as code injection or lateral movement

How to Mitigate CVE-2025-27481

Immediate Actions Required

• Apply the latest Microsoft security updates addressing CVE-2025-27481 immediately
• If patching is not immediately possible, consider disabling the Telephony Service on systems where it is not required
• Restrict network access to affected services using firewall rules
• Monitor affected systems for signs of exploitation attempts

Patch Information

Microsoft has released security updates to address this vulnerability. Administrators should consult the Microsoft Security Update Guide for CVE-2025-27481 for detailed patch information and download links specific to their affected Windows versions.

Patches are available for all supported Windows versions, including Windows 10, Windows 11, and Windows Server editions. Organizations should prioritize patching based on system exposure and criticality.

Workarounds

• Disable the Windows Telephony Service (TapiSrv) on systems that do not require telephony functionality
• Implement network segmentation to limit exposure of vulnerable services
• Enable Windows Defender Exploit Protection with Stack Protection enabled
• Use host-based firewalls to restrict access to TAPI services from untrusted networks

# Disable Windows Telephony Service (if not required)
sc config TapiSrv start= disabled
sc stop TapiSrv

# Verify service is stopped
sc query TapiSrv