CVE-2025-5555: Wincor Nixdorf PORT IO Buffer Overflow Flaw

CVE-2025-5555 Overview

CVE-2025-5555 is a stack-based buffer overflow in the Wincor Nixdorf PORT IO Driver up to version 1.0.0.1. The flaw resides in the sub_11100 function within the wnport.sys kernel driver and is reachable through the driver's IOCTL handler. A local, authenticated attacker can send a crafted IOCTL request to trigger memory corruption in kernel space. Successful exploitation can lead to arbitrary code execution with kernel privileges or a system crash. The issue is tracked under [CWE-119] and has been publicly disclosed. The vendor released a fix in version 3.0.0.1.

Critical Impact
Local attackers with low privileges can corrupt kernel memory through wnport.sys IOCTLs, enabling privilege escalation to SYSTEM on affected point-of-sale and ATM endpoints.

Affected Products

Wincor Nixdorf PORT IO Driver up to version 1.0.0.1
wnport.sys kernel driver (IOCTL handler component)
Diebold Nixdorf endpoints shipping the vulnerable PORT IO Driver

Discovery Timeline

2025-10-18 - CVE-2025-5555 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-5555

Vulnerability Analysis

The vulnerability affects wnport.sys, a Windows kernel-mode driver used by Wincor Nixdorf PORT IO software for hardware interaction on point-of-sale and ATM systems. The driver exposes an IOCTL interface to user-mode processes. When a request reaches the internal handler sub_11100, attacker-influenced input is copied onto a fixed-size stack buffer without adequate bounds checking. This classic stack-based buffer overflow [CWE-119] corrupts adjacent stack memory, including saved return addresses and structured exception handler records in the kernel stack.

Because the code executes in ring 0, memory corruption directly threatens system integrity. Exploitation can pivot into arbitrary kernel code execution, giving the attacker SYSTEM privileges, or produce a bugcheck that halts the machine. The driver is typically installed on retail and banking endpoints, which increases the operational impact of a successful exploit.

Root Cause

The root cause is missing input length validation in sub_11100 before copying user-supplied IOCTL buffer data onto the kernel stack. The handler trusts the caller-supplied size or terminator, allowing writes past the destination buffer. Public analysis of the flaw is available in the IAKB technical writeup and VulDB #329013 analysis.

Attack Vector

Exploitation requires local access and low privileges. An attacker running code on the target host opens a handle to the wnport device object and issues a DeviceIoControl call with an oversized input buffer aimed at the affected IOCTL. No user interaction is required. Network exploitation is not possible, but any code path that yields local execution — a malicious installer, a compromised service account, or a foothold from a prior intrusion — becomes a route to kernel-level compromise.

The vulnerability is described in prose because no verified public exploit code is referenced by NVD. Consult the IAKB writeup for reverse-engineering details.

Detection Methods for CVE-2025-5555

Indicators of Compromise

Presence of wnport.sys at version 1.0.0.1 or earlier on endpoints running Wincor Nixdorf PORT IO software.
Unexpected DeviceIoControl calls to the \\.\wnport device from non-vendor processes.
Kernel bugchecks (BSOD) referencing wnport.sys in crash dumps or WER telemetry.
New or unsigned processes issuing IOCTLs shortly before privilege escalation events on POS or ATM hosts.

Detection Strategies

Inventory kernel drivers across the fleet and flag hosts running wnport.sys below version 3.0.0.1.
Alert on non-allowlisted user-mode processes opening handles to the wnport device object.
Correlate kernel crashes involving wnport.sys with recent process creation events to identify exploitation attempts.
Monitor for local privilege escalation patterns: an unprivileged process spawning SYSTEM-level children after driver interaction.

Monitoring Recommendations

Ingest Windows kernel dump telemetry and Sysmon Event ID 6 (driver loaded) into your SIEM to track wnport.sys versions.
Enable audit logging for DeviceIoControl access to third-party device objects on POS and ATM endpoints.
Track integrity of the wnport.sys file hash against the vendor-published 3.0.0.1 baseline.

How to Mitigate CVE-2025-5555

Immediate Actions Required

Upgrade the Wincor Nixdorf PORT IO Driver to version 3.0.0.1 or later on all affected endpoints.
Restrict local logon and remote interactive access on POS and ATM systems to a minimal set of service accounts.
Enforce application allowlisting so only vendor binaries can open handles to the wnport device.
Review recent kernel crash reports involving wnport.sys and treat matches as potential exploitation attempts.

Patch Information

The vendor fixed CVE-2025-5555 in Wincor Nixdorf PORT IO Driver version 3.0.0.1. Updated packages are available from the Diebold Nixdorf Download Center. Additional advisory context is documented in VulDB #329013 details.

Workarounds

Where immediate patching is not feasible, remove or disable the wnport.sys driver on systems that do not require PORT IO functionality.
Apply Windows Defender Application Control or AppLocker policies to block untrusted binaries from executing on affected endpoints.
Segment POS and ATM networks to limit lateral movement paths that would allow an attacker to reach the local exploit prerequisite.

bash

# Query installed driver version on Windows
sc query wnport
powershell -Command "Get-Item C:\Windows\System32\drivers\wnport.sys | Select-Object VersionInfo"

# Disable the driver until the 3.0.0.1 update is deployed
sc config wnport start= disabled