CVE-2026-35423: Windows 11 Telnet Client Information Disclosure Vulnerability

Overview

Severity

Medium (CVSS 5.4)

CVSS Vector

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

Category

Information Disclosure

Exploit Status

Not Exploited

Exploitation Likelihood

Unlikely

Patch Tuesday

2026-May

Released

2026-05-12

Description

Out-of-bounds read in Telnet Client allows an unauthorized attacker to disclose information over a network.

FAQ

According to the CVSS metrics, successful exploitation of this vulnerability could lead to some loss of confidentiality (C:L), no loss to integrity (I:N) and lead to some loss of availability (A:L). What is the impact of this vulnerability? Successful exploitation of this vulnerability could allow an attacker to access limited sensitive information from system memory and may cause intermittent interruptions or reduced performance in the affected application. However, it would not allow the attacker to modify data. What type of information could be disclosed by this vulnerability? An attacker could potentially read limited portions of memory from the affected system, which may include sensitive information being processed by the Telnet client at the time of the connection. According to the CVSS metric, user interaction is required (UI:R). What interaction would the user have to do? For this vulnerability to be exploited, a user would need to initiate a Telnet connection to a malicious or compromised server, allowing specially crafted authentication responses to be processed by the Telnet client. Successful exploitation requires a user to take an action before the vulnerability can be triggered.

Affected Products (31)

Windows

• Windows 10 Version 1809 for 32-bit Systems
• Windows 10 Version 1809 for x64-based Systems
• Windows Server 2019
• Windows Server 2019 (Server Core installation)
• Windows Server 2022
• Windows Server 2022 (Server Core installation)
• Windows 10 Version 21H2 for 32-bit Systems
• Windows 10 Version 21H2 for ARM64-based Systems
• Windows 10 Version 21H2 for x64-based Systems
• Windows Server 2025 (Server Core installation)
• Windows 11 Version 25H2 for ARM64-based Systems
• Windows 11 Version 25H2 for x64-based Systems
• Windows 11 Version 23H2 for ARM64-based Systems
• Windows 11 Version 23H2 for x64-based Systems
• Windows Server 2022, 23H2 Edition (Server Core installation)
• Windows 11 Version 24H2 for ARM64-based Systems
• Windows 11 Version 24H2 for x64-based Systems
• Windows Server 2025
• Windows 11 version 26H1 for x64-based Systems
• Windows 11 Version 26H1 for ARM64-based Systems
• Windows 10 Version 1607 for 32-bit Systems
• Windows 10 Version 1607 for x64-based Systems
• Windows Server 2016
• Windows Server 2016 (Server Core installation)

ESU

• Windows 10 Version 22H2 for x64-based Systems
• Windows 10 Version 22H2 for ARM64-based Systems
• Windows 10 Version 22H2 for 32-bit Systems
• Windows Server 2012
• Windows Server 2012 (Server Core installation)
• Windows Server 2012 R2
• Windows Server 2012 R2 (Server Core installation)

Security Updates (14)

• 5087538
• 5087545
• 5087424
• 5087544
• 5087539
• 5087423
• 5089549
• 5089466
• 5087420
• 5087541
• 5089548
• 5087537
• 5087470
• 5087471

Acknowledgments

Microsoft

Revision History

• 2026-05-12: Information published.