CVE-2026-59117

Executive Summary

CVE-2026-59117 is a critical integer overflow or wraparound vulnerability in Windows Terminal that allows an unauthorized attacker to execute arbitrary code over a network. The flaw resides in how the terminal handles certain integer arithmetic operations, leading to memory corruption and potential remote code execution (RCE). With a CVSS score of 7.5, the vulnerability is exploitable without authentication and requires no user interaction, making it a high-priority threat for organizations using Windows Terminal. No public proof-of-concept (PoC) or exploit code is currently available, and the vendor has not yet released a patch. The EPSS score of 0.0% suggests low exploitation activity in the wild, but the risk remains significant due to the potential for network-based attacks.

Supply Chain & Package Security

Windows Terminal is a Microsoft product distributed via the Microsoft Store, GitHub releases, and Windows Update. This vulnerability does not affect NPM, PyPI, Go, or Ruby packages. However, organizations should verify the integrity of their Windows Terminal installations and monitor for any unofficial patches or workarounds.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Base Score: 7.5 (High)
• Attack Vector: Network (AV:N) – Exploitable remotely over a network.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Impact confined to the vulnerable component.
• Confidentiality Impact: High (C:H) – Potential data exposure.
• Integrity Impact: High (I:H) – Potential data modification.
• Availability Impact: High (A:H) – Potential denial of service or system crash.

Threat Level: High – Remote code execution with no authentication or user interaction.

Deep Dive & Mechanics

The vulnerability is an integer overflow or wraparound (CWE-190) in Windows Terminal’s handling of network data. When processing specially crafted network packets, the terminal performs arithmetic operations on integer values without proper bounds checking. An attacker can trigger an overflow that leads to a buffer overflow or memory corruption, allowing arbitrary code execution in the context of the terminal process.

Root Cause:
The terminal’s input parsing logic fails to validate integer sizes before performing operations like addition or multiplication. For example, if a packet contains a length field that is manipulated to cause an integer wraparound, the terminal may allocate a smaller buffer than needed, leading to a heap-based buffer overflow.

Attack Vector:
An attacker sends a malicious network packet to a system running Windows Terminal. The terminal processes the packet, triggering the integer overflow, which corrupts memory and allows the attacker to execute arbitrary code.

Impact:
Successful exploitation could allow an attacker to take full control of the affected system, install malware, or pivot to other network resources.

Vulnerable vs. Patched Code

Since no official patch is available, the following is a hypothetical comparison based on the vulnerability type.

Vulnerable Code (C-style pseudocode):

void process_packet(char *data, int length) {
    int buffer_size = length + 100; // Potential integer overflow
    char *buffer = malloc(buffer_size);
    if (buffer == NULL) return;
    memcpy(buffer, data, length);
    // Process buffer...
}

Patched Code (Hypothetical fix):

void process_packet(char *data, int length) {
    if (length < 0 || length > MAX_PACKET_SIZE) return; // Input validation
    size_t buffer_size = (size_t)length + 100;
    if (buffer_size < (size_t)length) return; // Check for overflow
    char *buffer = malloc(buffer_size);
    if (buffer == NULL) return;
    memcpy(buffer, data, length);
    // Process buffer...
}

The patched version adds input validation and overflow checks before memory allocation.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Windows Terminal installed on a target system.
• Network access to the target (e.g., same subnet or via a service that forwards packets to the terminal).
• No public exploit code available; this section provides a conceptual approach.

Exploitation Steps:

1. Reconnaissance: Identify systems running Windows Terminal (e.g., via Shodan dorks: "Windows Terminal", "wsl host").
2. Craft Payload: Create a network packet that triggers the integer overflow. The packet should include a manipulated length field that causes a wraparound.
3. Send Packet: Use a tool like netcat or a custom Python script to send the malicious packet to the target’s terminal service.
4. Execute Code: The overflow corrupts memory, allowing the attacker to inject shellcode that executes a reverse shell or other payload.

Example Python script (conceptual):

import socket

target_ip = "192.168.1.100"
target_port = 8080  # Example port

# Craft packet with integer overflow trigger
packet = b"\x00" * 100  # Placeholder
# Manipulate length field to cause overflow
# ...

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
sock.send(packet)
sock.close()

Blue Team (Defensive)

Detection:

• Monitor for unusual network traffic to Windows Terminal ports.
• Use the Sigma and Suricata rules provided in the Detection Engineering section.
• Enable Windows Event Logging for terminal processes.

Mitigation:

• Disable Windows Terminal if not needed.
• Use network segmentation to limit exposure.
• Apply vendor patches when available.
• Implement application whitelisting to prevent unauthorized code execution.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Unusual packets targeting Windows Terminal ports (e.g., 8080, 9090).
  • Packets with abnormally large or manipulated length fields.
• Host IOCs:
  • Unexpected crashes or memory errors in Windows Terminal.
  • Unusual child processes spawned by Windows Terminal (e.g., cmd.exe, powershell.exe).
  • Registry modifications related to terminal settings.
• File IOCs:
  • Temporary files created in %TEMP% with suspicious names.
  • Modified terminal configuration files.

Detection Engineering

YARA Rule

rule CVE_2026_59117_Windows_Terminal_Overflow {
    meta:
        description = "Detects potential integer overflow exploitation in Windows Terminal"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-59117"
    strings:
        $s1 = "WindowsTerminal.exe" ascii wide nocase
        $s2 = "overflow" ascii wide nocase
        $s3 = "length" ascii wide nocase
    condition:
        $s1 and ($s2 or $s3)
}

Sigma Rule

title: CVE-2026-59117 Windows Terminal Integer Overflow Exploitation
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects network traffic targeting Windows Terminal with potential integer overflow patterns
author: Valters IT
date: 2025-04-10
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        Image|endswith: 'WindowsTerminal.exe'
        Protocol: 'TCP'
        DestinationPort:
            - 8080
            - 9090
    condition: selection
falsepositives:
    - Legitimate terminal usage on non-standard ports
level: high

Suricata Rule

alert tcp any any -> any 8080,9090 (msg:"CVE-2026-59117 Windows Terminal Integer Overflow Attempt"; flow:to_server; content:"|00 00 00 00|"; depth:4; offset:0; reference:cve,2026-59117; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Windows Terminal if not required for business operations.
2. Network Segmentation: Restrict access to Windows Terminal services to trusted networks only.
3. Monitor Logs: Enable detailed logging for terminal processes and network connections.

Long-Term Fixes:

• Apply vendor patches as soon as they are released.
• Implement input validation and bounds checking in custom applications that interact with Windows Terminal.
• Use application whitelisting to prevent unauthorized code execution.

Workarounds:

• Use alternative terminal emulators (e.g., PowerShell ISE, ConEmu) until a patch is available.
• Configure firewalls to block inbound connections to Windows Terminal ports.

Valters IT
Securing Digital Frontiers