CVE-2025-49734: Microsoft PowerShell Privilege Escalation

CVE-2025-49734 Overview

CVE-2025-49734 is a local privilege escalation vulnerability in Windows PowerShell. The flaw stems from improper restriction of a communication channel to intended endpoints [CWE-923]. An authorized attacker with local access and low privileges can leverage this weakness to elevate privileges on affected Windows systems.

Microsoft published the advisory on September 9, 2025. The vulnerability affects a broad range of client and server Windows versions, including Windows 10, Windows 11, and Windows Server editions from 2016 through 2025. Exploitation requires local access and high attack complexity, but successful exploitation compromises confidentiality, integrity, and availability.

Critical Impact
A locally authenticated attacker can escalate privileges through PowerShell's exposed communication channel, gaining higher-privileged execution across supported Windows and Windows Server versions.

Affected Products

Microsoft PowerShell
Microsoft Windows 10 (1607, 1809, 21H2, 22H2) and Windows 11 (22H2, 23H2, 24H2)
Microsoft Windows Server 2016, 2019, 2022, 2022 23H2, and 2025

Discovery Timeline

2025-09-09 - CVE-2025-49734 published to NVD
2025-09-09 - Microsoft releases security update via MSRC advisory
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-49734

Vulnerability Analysis

The vulnerability is classified under [CWE-923]: Improper Restriction of Communication Channel to Intended Endpoints. Windows PowerShell exposes a communication channel that does not adequately validate or restrict which endpoints can interact with it. A local, authenticated attacker with low privileges can connect to this channel and interact with a higher-privileged PowerShell component.

Successful exploitation results in full compromise of confidentiality, integrity, and availability on the targeted host. The attack does not require user interaction, but the attack complexity is high, indicating that specific runtime conditions or race windows must be met for reliable exploitation.

Root Cause

The root cause is improper endpoint restriction on a PowerShell inter-process communication channel. PowerShell trusts communication from endpoints that should not be authorized to invoke privileged operations. This trust boundary weakness allows a lower-privileged process to influence a higher-privileged PowerShell context.

Attack Vector

The attack vector is local. The attacker must already possess valid credentials or an execution foothold on the target system, such as an interactive session, a compromised standard user account, or code execution within a lower-privileged process. From that position, the attacker interacts with the exposed PowerShell channel to trigger operations that execute with elevated privileges. Refer to the Microsoft CVE-2025-49734 Advisory for vendor-provided technical details.

Detection Methods for CVE-2025-49734

Indicators of Compromise

Unexpected powershell.exe or pwsh.exe child processes spawning from low-privileged user contexts followed by SYSTEM or administrator-level activity.
Anomalous named pipe or IPC connections targeting PowerShell host processes from non-administrative sessions.
PowerShell script block logs showing invocation of privileged cmdlets from unexpected callers.

Detection Strategies

Enable PowerShell script block logging (Event ID 4104) and module logging to capture the full command payload delivered through the abused channel.
Correlate Windows Security Event ID 4688 process creation events with parent-child process lineage that crosses privilege boundaries via PowerShell.
Hunt for local privilege escalation patterns where a standard user token precedes a SYSTEM token within the same process tree.

Monitoring Recommendations

Monitor and baseline PowerShell remoting, WSMan, and named pipe endpoints on servers and workstations.
Alert on any local-only PowerShell session that transitions from a medium-integrity process to a high or system-integrity process.
Ingest Windows PowerShell operational logs into a central SIEM or data lake and retain them for incident review.

How to Mitigate CVE-2025-49734

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2025-49734 Advisory to all affected Windows client and server systems.
Prioritize patching of multi-user systems, jump hosts, and terminal servers where local accounts have shell access.
Audit local accounts and remove unnecessary interactive logon rights on servers and privileged workstations.

Patch Information

Microsoft addresses CVE-2025-49734 through the Patch Tuesday updates published on September 9, 2025. Administrators should deploy the cumulative updates for each affected Windows 10, Windows 11, and Windows Server version. Consult the vendor advisory for the specific KB article that maps to each build.

Workarounds

Restrict local logon rights so that only trusted administrators can obtain an interactive session on sensitive hosts.
Enforce Constrained Language Mode and Just Enough Administration (JEA) on PowerShell endpoints to limit what authenticated users can invoke.
Enable AppLocker or Windows Defender Application Control policies to constrain execution of unsigned or untrusted PowerShell scripts.

bash

# Verify PowerShell language mode and enforce ConstrainedLanguage for standard users
$ExecutionContext.SessionState.LanguageMode

# Example: set the system-wide policy via environment variable (per-user contexts)
[Environment]::SetEnvironmentVariable('__PSLockdownPolicy','4','Machine')

# Enable PowerShell script block logging via registry
New-Item -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows\PowerShell\ScriptBlockLogging' -Force
Set-ItemProperty -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows\PowerShell\ScriptBlockLogging' -Name 'EnableScriptBlockLogging' -Value 1