CVE-2025-41732: Wago 0852-1328 Firmware RCE Vulnerability

CVE-2025-41732 Overview

CVE-2025-41732 is a critical stack-based buffer overflow vulnerability affecting Wago industrial Ethernet switches. An unauthenticated remote attacker can abuse unsafe sscanf calls within the check_cookie() function to write arbitrary data into fixed-size stack buffers, leading to full device compromise.

This vulnerability is classified under CWE-121 (Stack-based Buffer Overflow) and CWE-787 (Out-of-bounds Write), representing a severe threat to industrial control system environments where Wago devices are deployed.

Critical Impact

Unauthenticated attackers can achieve full device compromise by exploiting unsafe memory operations in the cookie validation function, potentially allowing complete control over affected industrial network infrastructure.

Affected Products

• Wago 0852-1328 Firmware
• Wago 0852-1328 Hardware
• Wago 0852-1322 Firmware
• Wago 0852-1322 Hardware

Discovery Timeline

• December 10, 2025 - CVE-2025-41732 published to NVD
• December 19, 2025 - Last updated in NVD database

Technical Details for CVE-2025-41732

Vulnerability Analysis

The vulnerability resides in the check_cookie() function, which is responsible for validating session cookies in the device's web management interface. The function uses unsafe sscanf calls to parse user-supplied cookie data without proper bounds checking, allowing attackers to overflow stack-allocated buffers.

When processing malicious cookie data, the sscanf function writes beyond the boundaries of fixed-size stack buffers. This memory corruption can overwrite critical stack elements including return addresses and saved registers, enabling attackers to hijack program execution flow.

The network-accessible nature of this vulnerability, combined with no authentication requirement and no user interaction needed, makes it particularly dangerous for exposed industrial devices. Successful exploitation grants attackers complete control over the device, including the ability to execute arbitrary code with device-level privileges.

Root Cause

The root cause is improper input validation in the check_cookie() function. The code uses sscanf with format specifiers that do not include width limiters, allowing unbounded writes to fixed-size stack buffers. When a cookie value exceeds the allocated buffer size, the sscanf function continues writing past the buffer boundary, corrupting adjacent stack memory.

This represents a classic stack-based buffer overflow pattern where user-controlled input is copied to a stack buffer without validating that the input length does not exceed the destination buffer capacity.

Attack Vector

The attack vector is network-based and requires no authentication. An attacker can craft a malicious HTTP request containing an oversized or specially formatted cookie value targeting the check_cookie() function. The exploitation process involves:

1. Sending an HTTP request to the device's web management interface
2. Including a malicious cookie header with payload data exceeding buffer boundaries
3. Overwriting stack memory including return addresses
4. Redirecting execution flow to attacker-controlled code

The vulnerability can be exploited by constructing a cookie value that precisely overwrites the return address on the stack, enabling the attacker to redirect execution to shellcode or ROP gadgets present in the firmware.

Detection Methods for CVE-2025-41732

Indicators of Compromise

• Unusual HTTP requests to Wago device management interfaces containing abnormally large cookie values
• Unexpected device behavior, crashes, or reboots following web interface access
• Modified device configurations or firmware without authorized changes
• Network traffic anomalies indicating command-and-control communications from industrial devices

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with oversized cookie headers targeting Wago devices
• Monitor web server logs on Wago devices for requests with abnormally large cookie values
• Deploy application-layer firewalls to inspect and block malformed HTTP requests to industrial device management interfaces
• Use behavioral analysis to detect unusual process execution or memory access patterns on affected devices

Monitoring Recommendations

• Establish baseline network behavior for Wago industrial switches and alert on deviations
• Configure logging for all web management interface access attempts
• Monitor for unexpected outbound connections from industrial network segments
• Implement periodic integrity verification of device firmware and configurations

How to Mitigate CVE-2025-41732

Immediate Actions Required

• Restrict network access to device management interfaces using network segmentation and access control lists
• Disable web management interfaces if not operationally required
• Place affected devices behind properly configured firewalls blocking untrusted access
• Review network logs for evidence of exploitation attempts

Patch Information

Organizations should consult the CERT-VDE Security Advisory VDE-2025-095 for official patch information and firmware updates from Wago. Ensure firmware is updated to the latest version that addresses CVE-2025-41732.

Workarounds

• Implement strict network segmentation to isolate affected devices from untrusted networks
• Deploy web application firewalls or reverse proxies to filter and sanitize HTTP requests before they reach the device
• Disable the web management interface entirely and use alternative management methods if available
• Apply access control lists limiting management interface access to specific trusted IP addresses

# Example network access control configuration
# Restrict management interface access to trusted management network
iptables -A INPUT -p tcp --dport 80 -s 10.0.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 10.0.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP