CVE-2026-89207: Siemens WTV Web Interface DOS Vulnerability

CVE-2026-89207 Overview

CVE-2026-89207 affects the Siemens WTV676-HB6035 and WTV776-HB6035 web interfaces. The devices fail to properly validate input received from backend services [CWE-1287]. An unauthenticated remote attacker can exploit this weakness to force the device into protection mode. Entering protection mode disables the web access function and removes remote connectivity to the device.

Siemens documented the issue in advisory SSA-823812. The flaw impacts availability of the management interface but does not directly compromise data confidentiality. Fixed firmware is available in WTV676-HB6035 V3.94 and WTV776-HB6035 V4.17.

Critical Impact
Unauthenticated network attackers can trigger a protection-mode transition that disables the web management interface, disrupting remote administration until manual recovery.

Affected Products

Siemens WTV676-HB6035 Web Interface, all versions prior to V3.94
Siemens WTV776-HB6035 Web Interface, all versions prior to V4.17

Discovery Timeline

2026-09-16 - CVE-2026-89207 published to the National Vulnerability Database
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-89207

Vulnerability Analysis

The vulnerability resides in the web interface of two Siemens WTV-series devices. The interface accepts data from backend services without applying proper validation on the received input. An attacker who can reach the device over the network can send crafted input that the web interface forwards or processes without verifying its integrity or expected structure.

Processing this input causes the device to transition into protection mode. Protection mode is a defensive state in which the device restricts operations to preserve safety. In this state, the web access function becomes unavailable, and remote administrators lose the ability to configure or monitor the device through the web interface.

The issue is classified under CWE-1287: Improper Validation of Specified Type of Input. No authentication or user interaction is required to trigger the condition.

Root Cause

The web interface trusts data returned from backend services without verifying that the input conforms to expected types, formats, or value ranges. When malformed or unexpected input reaches internal logic that governs device state, the device interprets the anomaly as a fault condition and activates protection mode.

Attack Vector

Exploitation occurs over the network against the device web interface. The attacker sends input that the web interface passes to state-management logic without proper validation. No credentials are needed. The resulting protection-mode transition disables the web interface, producing a denial-of-service condition against remote management. Recovery typically requires local intervention or a device reset per vendor guidance.

No public proof-of-concept code has been published, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-89207

Indicators of Compromise

Sudden loss of web interface reachability on WTV676-HB6035 or WTV776-HB6035 devices without a corresponding network or power event
Device status indicators reporting protection mode following inbound HTTP/HTTPS traffic from unexpected sources
Repeated malformed HTTP requests to the device management interface preceding the outage

Detection Strategies

Baseline normal HTTP request patterns to the device web interface and alert on anomalous payload structures or unexpected content types
Correlate device availability changes with recent management-interface traffic to identify externally triggered protection-mode transitions
Enumerate WTV676-HB6035 and WTV776-HB6035 firmware versions across the environment to identify assets running versions below V3.94 and V4.17 respectively

Monitoring Recommendations

Forward device syslog and web interface access logs to a centralized SIEM for correlation with network telemetry
Monitor firewall and network sensors for unauthorized inbound connections to the device management interface
Track device uptime and protection-mode state transitions as availability metrics reviewed by operations teams

How to Mitigate CVE-2026-89207

Immediate Actions Required

Update WTV676-HB6035 devices to firmware V3.94 or later and WTV776-HB6035 devices to V4.17 or later
Restrict network access to the device web interface using firewall rules that allow only trusted management hosts
Place affected devices on segmented management networks isolated from general user and internet-facing traffic
Review device recovery procedures so operators can quickly restore service if a protection-mode event occurs

Patch Information

Siemens has released fixed firmware addressing CVE-2026-89207. Upgrade WTV676-HB6035 to V3.94 or later, and WTV776-HB6035 to V4.17 or later. Refer to the Siemens Security Advisory SSA-823812 for full remediation guidance and download instructions.

Workarounds

Limit access to the web interface to a defined allowlist of administrative IP addresses
Deploy the device behind a network segmentation boundary that blocks untrusted inbound connections
Disable remote access to the web interface when it is not actively required for administration

bash

# Example firewall allowlist restricting web interface access to management subnet
iptables -A INPUT -p tcp --dport 443 -s 10.10.20.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP
iptables -A INPUT -p tcp --dport 80 -s 10.10.20.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP