CVE-2025-29828Network attack vector

Unauthenticated code execution via fragmented ClientHello messages

Published Jun 10, 2025 · Updated Feb 26, 2026

Windows Schannel allows remote attackers to execute arbitrary code by sending malicious fragmented TLS ClientHello messages. Schannel retains memory beyond its effective lifetime while processing the fragmented handshake messages instead of releasing it. Exploitation requires a TLS-accepting server and a large number of messages, but no authentication or user interaction.

CVSS severity8.1
High
EPSS probability1.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Windows Schannel allows remote attackers to execute arbitrary code by sending malicious fragmented TLS ClientHello messages. Schannel retains memory beyond its effective lifetime while processing the fragmented handshake messages instead of releasing it. Exploitation requires a TLS-accepting server and a large number of messages, but no authentication or user interaction.

The record

CVE
CVE-2025-29828
Published
Jun 10, 2025
Updated
Feb 26, 2026
Vendor
Microsoft
Product
Windows Server 2025 (Server Core installation)
Classifications
CWE-401, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 10, 2025CVE publishedPublication date reported by the CVE source.
  2. Feb 26, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.0.26100.0 <10.0.26100.4349

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Windows Server 2025 (Server Core installation)version=10.0.26100.0 <10.0.26100.4349
Microsoft · Windows 11, version 24H2version=10.0.26100.0 <10.0.26100.4349
Microsoft · Windows Server 2022, 23H2 Edition (Server Core installation)version=10.0.25398.0 <10.0.25398.1665
Microsoft · Windows 11 Version 22H3version=10.0.22631.0 <10.0.22631.5472
Microsoft · Windows 11 Version 23H2version=10.0.22631.0 <10.0.22631.5472
Microsoft · Windows 11, version 22H2version=10.0.22621.0 <10.0.22621.5472
Microsoft · Windows Server 2022version=10.0.20348.0 <10.0.20348.3807
Microsoft · Windows Server 2025version=10.0.26100.0 <10.0.26100.4349

Published CVSS scores

8.1Microsoft CorporationCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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