CVE-2026-42981: Windows Performance Monitor RCE Flaw

CVE-2026-42981 Overview

CVE-2026-42981 is an integer underflow vulnerability [CWE-191] in Windows Performance Monitor. The flaw allows an unauthenticated attacker to execute arbitrary code over a network. Microsoft published the advisory on June 9, 2026, and it carries a CVSS 3.1 base score of 8.1 with the vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. Exploitation requires no privileges and no user interaction, though attack complexity is high. Successful exploitation results in full loss of confidentiality, integrity, and availability on the targeted host.

Critical Impact

Unauthenticated remote code execution against Windows Performance Monitor with full system-level impact across confidentiality, integrity, and availability.

Affected Products

• Windows Performance Monitor (specific Windows versions listed in the Microsoft Security Update for CVE-2026-42981)

Discovery Timeline

• 2026-06-09 - CVE-2026-42981 published to NVD
• 2026-06-09 - Last updated in NVD database

Technical Details for CVE-2026-42981

Vulnerability Analysis

The vulnerability resides in Windows Performance Monitor, a built-in Windows component used to collect and analyze system performance data. The flaw is classified as an integer underflow (wrap or wraparound) condition under [CWE-191]. An unauthenticated attacker reaching the affected service over a network can trigger the underflow to corrupt memory and execute arbitrary code. The EPSS model assigns a low near-term exploitation probability, but the unauthenticated network reach and remote code execution outcome justify prompt remediation.

Root Cause

The root cause is improper validation of a signed or unsigned numeric value during data processing inside Windows Performance Monitor. When the value is decremented below its minimum bound, it wraps around to a very large number. Downstream allocation or length calculations then operate on the wrapped value, producing an undersized buffer or oversized copy length. The result is out-of-bounds memory access that an attacker can shape into controlled code execution.

Attack Vector

The attack vector is network-based. An attacker sends a crafted request to a system exposing Windows Performance Monitor functionality. Attack complexity is high, indicating the attacker must win a race condition or satisfy specific environmental preconditions to reliably trigger the underflow. No authentication or user interaction is required. Refer to the Microsoft Security Update for CVE-2026-42981 for protocol-level specifics.

Detection Methods for CVE-2026-42981

Indicators of Compromise

• Unexpected crashes or restarts of Windows Performance Monitor processes such as perfmon.exe or related services.
• Anomalous network connections to Performance Monitor or Performance Counter remote interfaces from untrusted segments.
• Spawning of child processes (e.g., cmd.exe, powershell.exe) from Performance Monitor process trees.

Detection Strategies

• Monitor Windows Event Logs for crash, fault, and Watson reports tied to Performance Monitor binaries.
• Inspect network telemetry for inbound traffic to Remote Performance Counter RPC interfaces from outside expected administrative ranges.
• Hunt for process lineage anomalies where Performance Monitor components launch shells, scripting hosts, or LOLBins.

Monitoring Recommendations

• Enable verbose logging on hosts that expose Performance Monitor remotely and forward events to a centralized SIEM.
• Baseline normal remote performance-counter usage and alert on deviations in source IP, frequency, or payload size.
• Apply MITRE ATT&CK mappings for Initial Access (T1190) and Execution (T1203) to triage related alerts.

How to Mitigate CVE-2026-42981

Immediate Actions Required

• Apply the Microsoft security update referenced in the MSRC advisory for CVE-2026-42981 to all affected Windows systems.
• Inventory hosts that expose Windows Performance Monitor over the network and prioritize them for patching.
• Restrict inbound access to Performance Monitor and remote performance-counter interfaces to trusted management subnets.

Patch Information

Microsoft has released an official fix. Consult the Microsoft Security Update for CVE-2026-42981 for the specific KB articles, affected builds, and update packages applicable to your Windows version. Deploy the update through Windows Update, WSUS, Microsoft Update Catalog, or your enterprise patch management platform.

Workarounds

• Block inbound network access to Performance Monitor RPC endpoints at the host firewall and perimeter where remote monitoring is not required.
• Disable remote performance data collection on systems that do not require it.
• Segment management networks so only authorized monitoring servers can reach Performance Monitor interfaces.

# Example: restrict inbound RPC to Performance Monitor on Windows hosts
New-NetFirewallRule -DisplayName "Block Remote PerfMon" `
  -Direction Inbound `
  -Program "%SystemRoot%\System32\perfmon.exe" `
  -Action Block