CVE-2026-49177: Windows 10 1607 Information Disclosure Flaw

CVE-2026-49177 Overview

CVE-2026-49177 is an out-of-bounds read vulnerability in the Windows TCP/IP stack. The flaw allows an authenticated local attacker to read memory outside the intended buffer boundary, resulting in information disclosure. Microsoft assigned this issue a CVSS 3.1 base score of 5.5 and mapped it to CWE-125: Out-of-bounds Read.

The vulnerability affects a wide range of Windows client and server platforms, from Windows Server 2012 through the newest Windows 11 24H2, 25H2, and 26H1 builds, and Windows Server 2025. Exploitation requires local access and low privileges, and no user interaction is needed.

Critical Impact
Successful exploitation leaks kernel or driver memory contents from the TCP/IP stack, exposing data that can support subsequent privilege escalation or bypass of address space layout randomization (ASLR).

Affected Products

Microsoft Windows 10 (1607, 1809, 21H2, 22H2) across x86, x64, and ARM64 editions
Microsoft Windows 11 24H2, 25H2, and 26H1 (x64 and ARM64)
Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025

Discovery Timeline

2026-07-14 - CVE-2026-49177 published to NVD
2026-07-17 - Last updated in NVD database

Technical Details for CVE-2026-49177

Vulnerability Analysis

The vulnerability resides in the Windows TCP/IP networking component, which is implemented primarily in the tcpip.sys kernel driver. An out-of-bounds read [CWE-125] occurs when the driver processes network-related data structures and reads memory beyond the allocated buffer boundary.

An authenticated local attacker can trigger the flawed code path and receive kernel memory contents in return. The disclosed data can include pointers, cryptographic material, or other sensitive kernel state. Attackers frequently chain such disclosures with a separate memory corruption bug to defeat kernel ASLR and achieve reliable privilege escalation.

The impact is limited to confidentiality. Integrity and availability are unaffected, and the attack cannot be launched remotely across the network despite the component name.

Root Cause

The root cause is missing or incorrect bounds validation on a buffer accessed by the TCP/IP stack. When a caller supplies input that references data beyond the allocated region, the driver returns adjacent memory contents rather than rejecting the request. Microsoft has not published detailed technical internals in the advisory.

Attack Vector

Exploitation is strictly local. The attacker must already have code execution on the target host with at least low-privilege user rights. No user interaction is required. The attacker invokes the vulnerable code path through a local interface exposed by the TCP/IP stack, typically an IOCTL sent to a networking device object or a socket-level operation, and reads back the leaked bytes.

The vulnerability is well suited to malware and post-exploitation tooling that seeks to escalate privileges after initial access from a phishing payload, a supply-chain implant, or a compromised low-privilege service account.

Detection Methods for CVE-2026-49177

Indicators of Compromise

Unexpected user-mode processes issuing repeated DeviceIoControl calls to TCP/IP-related device objects such as \Device\Tcp, \Device\Udp, or \Device\Nsi
Non-administrative processes performing atypical raw socket or Winsock kernel interface operations
Kernel memory disclosure artifacts, including leaked pointers appearing in user-mode process memory or exfiltrated data

Detection Strategies

Monitor for processes that access networking driver handles outside of normal application behavior, especially from unsigned or newly introduced binaries
Correlate suspicious IOCTL activity against TCP/IP device objects with subsequent privilege escalation attempts or credential access behavior
Apply behavioral analytics to identify low-privilege processes that exhibit kernel probing patterns typical of information disclosure exploitation chains

Monitoring Recommendations

Enable Windows kernel auditing and Event Tracing for Windows (ETW) providers covering TCP/IP and driver load events
Ingest endpoint telemetry into a centralized data lake to correlate driver interactions with process lineage and later stages of an attack chain
Track patch compliance on all Windows client and server systems listed in the affected products to identify unpatched hosts subject to local exploitation

How to Mitigate CVE-2026-49177

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-49177 advisory to all affected Windows and Windows Server systems
Prioritize patching of multi-user hosts, terminal servers, and jump boxes where low-privilege local access is most common
Audit local account access and remove unnecessary interactive logon rights on servers to reduce the pool of potential attackers

Patch Information

Microsoft has released cumulative updates addressing CVE-2026-49177 for all supported Windows and Windows Server versions listed above. Refer to the Microsoft Security Response Center advisory for KB article numbers and update packages specific to each build. Systems on Windows 10 1607, 1809, and Server 2012 that are outside standard support require Extended Security Updates (ESU).

Workarounds

No official workaround is published by Microsoft; applying the security update is the required remediation
Restrict local logon rights and enforce least-privilege on all Windows hosts to reduce the population of accounts capable of triggering the vulnerability
Enable application control policies such as Windows Defender Application Control (WDAC) or AppLocker to block unauthorized binaries from executing local exploitation code

bash

# Verify installed updates on a Windows host and confirm TCP/IP driver version
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10
Get-Item C:\Windows\System32\drivers\tcpip.sys | Select-Object VersionInfo