CVE-2025-21201 — Windows Telephony Server Remote Code Execution Vulnerability

Executive Summary

None

Overview

8.8

CVSS HIGH

Important

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Remote Code Execution

Weakness CWE-415: Double Free

Released Feb 11 2025

Last Updated Feb 11 2025

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.01792 — 0.76432 percentile

NVD CVSS 8.8 HIGH — matches MSRC

CVSS Vector

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

ATTACK VECTOR

Network

ATTACK COMPLEXITY

Low

PRIVILEGES REQUIRED

None

USER INTERACTION

Required

SCOPE

Unchanged

CONFIDENTIALITY

High

INTEGRITY

High

AVAILABILITY

High

EXPLOIT CODE MATURITY

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 7.7

EPSS Score

0.01792

probability of exploitation in the next 30 days

0.76432 percentile - updated 2026-08-14

View on FIRST.org

Affected Products

25 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 10 for 32-bit Systems	`5052040 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 for x64-based Systems	`5052040 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 1607 for 32-bit Systems	`5052006 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 1607 for x64-based Systems	`5052006 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 1809 for 32-bit Systems	`5052000 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 1809 for x64-based Systems	`5052000 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 21H2 for 32-bit Systems	`5051974 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 21H2 for ARM64-based Systems	`5051974 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 21H2 for x64-based Systems	`5051974 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 22H2 for 32-bit Systems	`5051974 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 22H2 for ARM64-based Systems	`5051974 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 22H2 for x64-based Systems	`5051974 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 22H2 for ARM64-based Systems	`5051989 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 22H2 for x64-based Systems	`5051989 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 23H2 for ARM64-based Systems	`5051989 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 23H2 for x64-based Systems	`5051989 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 24H2 for ARM64-based Systems 5051987 (Security Update) 5052105 (SecurityHotpatchUpdate) Important Remote Code Execution 5050009 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26100.3194 10.0.26100.3107 Yes None Windows 11 Version 24H2 for x64-based Systems 5051987 (Security Update) 5052105 (SecurityHotpatchUpdate) Important Remote Code Execution 5050009 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.26100.3194 10.0.26100.3107 Yes None Windows Server 2008 for 32-bit Systems Service Pack 2 5052038 (Monthly Rollup) 5052072 (Security Only) Important Remote Code Execution 5050063 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.0.6003.23117 Yes None Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 5052038 (Monthly Rollup) 5052072 (Security Only) Important Remote Code Execution 5050063 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.0.6003.23117 Yes None Windows Server 2008 for x64-based Systems Service Pack 2 5052038 (Monthly Rollup) 5052072 (Security Only) Important Remote Code Execution 5050063 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.0.6003.23117 Yes None Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 5052038 (Monthly Rollup) 5052072 (Security Only) Important Remote Code Execution 5050063 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.0.6003.23117 Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 5052016 (Monthly Rollup) 5052032 (Security Only) Important Remote Code Execution 5050049 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.1.7601.27566 Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 5052016 (Monthly Rollup) 5052032 (Security Only) Important Remote Code Execution 5050049 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 6.1.7601.27566 Yes None Windows Server 2012	`5052020 (Monthly Rollup)`	Important	Remote Code Execution	Yes
Windows Server 2012 (Server Core installation)	`5052020 (Monthly Rollup)`	Important	Remote Code Execution	Yes
Windows Server 2012 R2	`5052042 (Monthly Rollup)`	Important	Remote Code Execution	Yes
Windows Server 2012 R2 (Server Core installation)	`5052042 (Monthly Rollup)`	Important	Remote Code Execution	Yes
Windows Server 2016	`5052006 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2016 (Server Core installation)	`5052006 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2019	`5052000 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2019 (Server Core installation)	`5052000 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2022 5051979 (Security Update) 5052106 (SecurityHotpatchUpdate) Important Remote Code Execution 5049983 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.20348.3207 10.0.20348.3148 Yes None Windows Server 2022 (Server Core installation) 5051979 (Security Update) 5052106 (SecurityHotpatchUpdate) Important Remote Code Execution 5049983 Base: 8.8 Temporal: 7.7 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C 10.0.20348.3207 10.0.20348.3148 Yes None Windows Server 2022, 23H2 Edition (Server Core installation)	`5051980 (Security Update)`	Important	Remote Code Execution	Yes

Patches

8 patches

Article	Type	Restart
`5052040`	Security Update	Yes
`5052006`	Security Update	Yes
`5052000`	Security Update	Yes
`5051974`	Security Update	Yes
`5051989`	Security Update	Yes
`5052020`	Monthly Rollup	Yes
`5052042`	Monthly Rollup	Yes
`5051980`	Security Update	Yes

Patch Diff

ghidriff · remotesp.tsp (KB5051987)

Double free (CWE-415) in the Windows Telephony Server client-side TAPI Remote Service Provider remotesp.tsp, remote code execution on a client that connects to a malicious telephony server (Important, RCE, AV:N, UI:R, CVSS 8.8). remotesp.tsp issues async requests to a remote telephony server and processes its responses in RemoteDoFunc, which walks the returned per-request records and copies each record's data back into the corresponding client-side outstanding-request buffer selected from an array. PRE: a returned record was applied to its slot WITHOUT verifying it corresponded to that outstanding request, so a crafted server response could route a mismatched/duplicate completion to a request buffer it did not own, reprocessing/re-releasing a buffer whose lifetime had already ended - a double free. Because the client parses attacker-controlled server data over the network, the double free is an RCE primitive on the client. Correct binary identification: tapisrv.dll/tapi32.dll were unchanged (.3037) across Jan->Feb; remotesp.tsp went .2894 (KB5050094) -> .3194 (KB5051987), matching the MSRC fixed build exactly. Self-diff (ghidriff, --no-bsim) of remotesp.tsp 10.0.26100.2894 -> .3194 confirms the fix: RemoteDoFunc, gated behind CFR flag Feature_2332850489, adds an identity check (returned record's leading field must equal the target client buffer's leading field) and returns 0x80000048 on mismatch before the memcpy, so only a record matching its outstanding request is applied. Stated at confirmed-changed level (RemoteDoFunc is a broad refactor; the isolable mechanism is the added record-to-buffer identity validation).

Pre-patch version 10.0.26100.2894 Download

Post-patch version 10.0.26100.3194 Download

Function	Address	Change	Note
`RemoteDoFunc`	`code change`	code (adds returned-record identity check before applying to client buffer, CFR-gated)	Pre: server-returned records applied to client request buffers without verifying the record belonged to that buffer -> a crafted/duplicate response could re-release a buffer (double free). Post (Feature_2332850489): if (returned_record != *client_buf[slot]) return 0x80000048; before the memcpy, so only matching records are applied.
`RemoteSPAttach`	`code change`	code (server-init state guard added)	Reworked under Feature_3862983993 with an added guard on gpCurrInitServer state during attach.
`Feature_2332850489`	`gate`	added (CFR gate)	CFR flag gating the returned-record identity check in RemoteDoFunc; the original unchecked handling remains when the flag is disabled.

View full diff report View RCA report

Attack Path

A malicious telephony server returns a mismatched async-completion record, driving a double free on the client

Derived from the patch delta: the checks added by the vendor identify which fields crossed a trust boundary unvalidated. Reachability and privilege are taken from the call chain in the RCA report.

Exploits & PoC

No public exploit or PoC has been linked for this CVE yet. When available, references are sourced from public repositories and may be unverified or non-functional — review carefully before use.

Detection Rules

No public Sigma or Nuclei detection rule has been mapped to this CVE yet. Coverage is concentrated on exploited / high-profile vulnerabilities; check SigmaHQ for updates.

Acknowledgments

Anonymous

References

MSRC Advisory MITRE NVD