dbcve.org
Windows 10 1507Operating system · Microsoft

CVE-2025-21221

HIGH · 8.8 CVSS v3.1 Published 2025-04-08
Fix available
A fix is available. Upgrade to 10.0.10240.20978 / 10.0.14393.7969 or later.
See remediation →
95/100
Remediation priority · Urgent
Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Heap-based buffer overflow in Windows Telephony Service allows an unauthorized attacker to execute code over a network.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

Heap-based buffer overflow vulnerability in Windows Telephony Service that enables remote code execution by an unauthorized attacker over a network. The vulnerability stems from improper memory handling when the service processes certain inputs, allowing an attacker to overflow heap memory and inject malicious code.

MitigationApply the Microsoft security update for CVE-2025-21221 immediately. If immediate patching is not feasible, disable the Windows Telephony Service if not required by business operations, and enforce network segmentation to restrict access to affected systems.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Windows 10 1507Operating system
Affected:< 10.0.10240.20978
Windows 10 1607Operating system
Affected:< 10.0.14393.7969
Windows 10 1809Operating system
Affected:< 10.0.17763.7136
Windows 10 21h2Operating system
Affected:< 10.0.19044.5737
Windows 10 22h2Operating system
Affected:< 10.0.19045.5737
Windows 11 22h2Operating system
Affected:< 10.0.22621.5189
Windows 11 23h2Operating system
Affected:< 10.0.22631.5189
Windows 11 24h2Operating system
Affected:< 10.0.26100.3775

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Windows version and build number
    Run 'winver' or execute 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to retrieve the installed Windows version and build number
    Affected if The build number falls below the threshold for your Windows release (e.g., below 10.0.19045.5737 for Windows 10 22h2, below 10.0.22621.5189 for Windows 11 22h2)
  2. Check Telephony Service status
    Run 'Get-Service TapiSrv' in PowerShell or 'sc query TapiSrv' in Command Prompt to determine if the Windows Telephony Service is installed and running
    Affected if The service state shows as RUNNING, indicating the vulnerable component is active
  3. Verify service startup type
    Run 'sc qc TapiSrv' to query the service configuration and check the START_TYPE value
    Affected if The service is set to AUTO_START (type 10) or DEMAND_START, making it potentially reachable on the network
  4. Confirm network exposure of the service
    Review firewall rules or network configuration to determine if the Telephony Service port is accessible from untrusted networks. Use 'netsh advfirewall firewall show rule name=all' to list firewall rules
    Affected if Inbound network access to the Telephony Service is permitted from external or untrusted network segments

Your system is affected if it runs a Windows version with a build number lower than the patched threshold AND the Telephony Service (TapiSrv) is running and network-accessible.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 10.0.10240.20978 / 10.0.14393.7969 / 10.0.17763.7136 or later
Fixed in 10.0.10240.2097810.0.14393.796910.0.17763.7136
Interim mitigation

Apply the Microsoft security update for CVE-2025-21221 immediately. If immediate patching is not feasible, disable the Windows Telephony Service if not required by business operations, and enforce network segmentation to restrict access to affected systems.

Recommended fix High confidence

Install the latest Windows Security Update containing the CVE-2025-21221 fix (for Windows 10: KB number from February 2025 patch Tuesday; for Windows 11: corresponding KB update)

  1. Open Settings on the Windows system
  2. Navigate to Update & Security > Windows Update
  3. Click 'Check for updates' to download and install the latest security updates
  4. Ensure the update containing the fix for CVE-2025-21221 is installed (refer to Microsoft Security Guide MSRC for the specific KB number)
  5. Restart the system if prompted to complete the installation
  6. Verify the installed version matches or exceeds the fixed build version for your Windows release
Caveat Standard Windows update; may require restart; ensure backup of critical data before applying updates

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Windows 10 1507 Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,224.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2025-21221 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-21221 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data