CVE-2024-43620 Overview
CVE-2024-43620 is a remote code execution vulnerability in the Windows Telephony Service (TAPI). The flaw is a heap-based buffer overflow ([CWE-122]) that affects a broad range of Microsoft Windows client and server releases, from Windows 10 1507 through Windows 11 24H2 and Windows Server 2008 through Windows Server 2025. An attacker who tricks a user into connecting to a malicious server, or who lures a victim into invoking a specially crafted telephony request, can execute arbitrary code in the context of the target process.
Critical Impact
Successful exploitation grants attackers code execution on the target host with full impact to confidentiality, integrity, and availability across nearly all supported Windows versions.
Affected Products
- Microsoft Windows 10 (1507, 1607, 1809, 21H2, 22H2) on x86, x64, and ARM64
- Microsoft Windows 11 (22H2, 23H2, 24H2) on x64 and ARM64
- Microsoft Windows Server 2008, 2012, 2012 R2, 2016, 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- 2024-11-12 - CVE-2024-43620 published to NVD as part of Microsoft's November 2024 Patch Tuesday
- 2024-11-15 - Last updated in the NVD database
Technical Details for CVE-2024-43620
Vulnerability Analysis
The vulnerability resides in the Windows Telephony Service, which implements the Telephony Application Programming Interface (TAPI) used by applications for voice, fax, and modem communications. The defect is classified as a heap-based buffer overflow ([CWE-122]), meaning the service writes attacker-controlled data beyond the bounds of a dynamically allocated heap buffer. The exploit requires user interaction, indicating that a victim must perform an action such as initiating a telephony session or interacting with a malicious client or server.
Once the overflow occurs, attackers can corrupt adjacent heap structures, function pointers, or virtual table entries. This corruption can be steered toward arbitrary code execution within the Telephony Service process. The vulnerability is reachable over the network, which expands the attack surface beyond local exploitation scenarios.
Root Cause
The root cause is improper validation of the length or structure of attacker-controlled input processed by TAPI routines. When the service copies that input into a fixed-size heap buffer, it does not enforce the allocated boundary, allowing adjacent memory to be overwritten. The detailed cause has not been published by Microsoft beyond the heap-based overflow classification.
Attack Vector
The attacker delivers a crafted telephony payload or induces the victim to connect to a malicious endpoint that returns malformed TAPI responses. The Telephony Service parses the data, triggers the heap overflow, and executes shellcode or hijacks execution. Because the attack vector is network-based with low complexity and no privileges required, opportunistic phishing or watering-hole techniques are viable delivery mechanisms.
No public proof-of-concept exploit or in-the-wild exploitation has been confirmed, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS score places it in a higher-than-average likelihood band for future exploitation.
Detection Methods for CVE-2024-43620
Indicators of Compromise
- Unexpected crashes, restarts, or memory faults in TapiSrv.dll or the svchost.exe instance hosting the Telephony Service
- Outbound network connections from the Telephony Service process to untrusted or newly observed external hosts
- New child processes spawned by the Telephony Service host that do not match historical baselines
Detection Strategies
- Monitor Windows Error Reporting and crash dumps for faults referencing the Telephony Service or TAPI components
- Apply behavioral detection for process injection, code execution, or LOLBin invocation originating from svchost.exe -k NetworkService hosting TapiSrv
- Correlate inbound or outbound TAPI-related RPC traffic with anomalous endpoint activity
Monitoring Recommendations
- Enable EDR telemetry on service host processes and alert on unsigned module loads or memory allocations marked executable
- Track Windows Service state changes for the Telephony Service across the fleet to identify abnormal restarts
- Capture and review RPC interface enumeration attempts targeting telephony endpoints
How to Mitigate CVE-2024-43620
Immediate Actions Required
- Apply the November 2024 Microsoft security updates that address CVE-2024-43620 to all affected Windows client and server systems
- Inventory systems running the Telephony Service and prioritize patching internet-exposed or remote-access hosts first
- Restrict inbound network access to RPC endpoints associated with telephony to trusted management networks only
Patch Information
Microsoft released fixes for CVE-2024-43620 as part of the November 12, 2024 security update cycle. Refer to the Microsoft CVE-2024-43620 Advisory for the specific KB articles applicable to each Windows build and architecture. Deploy the appropriate cumulative update through Windows Update, WSUS, Microsoft Update Catalog, or your enterprise patch management tooling.
Workarounds
- Disable the Windows Telephony Service (TapiSrv) on systems where TAPI functionality is not required
- Block inbound RPC traffic to vulnerable hosts at the network perimeter and host firewall when patching cannot be performed immediately
- Enforce least-privilege user accounts and application allowlisting to limit post-exploitation impact pending patch deployment
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
