CVE-2025-41719: Webserver Auth Bypass Vulnerability

CVE-2025-41719 Overview

CVE-2025-41719 is a high-severity input validation flaw affecting a device webserver that manages user accounts. A low-privileged remote attacker can submit a sequence of unsupported characters that corrupts the webserver's user storage. The corruption deletes all previously configured user accounts and triggers the recreation of the default Administrator account with a known default password. The vulnerability is tracked under CWE-1286: Improper Validation of Syntactic Correctness of Input and was published on 2025-10-22 with details disclosed through a CERT VDE CSAF advisory.

Critical Impact
Successful exploitation removes all configured accounts and restores a default Administrator with publicly known credentials, granting an attacker full administrative control over the affected device.

Affected Products

Affected product details published in the CERT VDE advisory vde-2025-060
Device webserver management interface with user storage subsystem
Refer to the vendor advisory for specific impacted firmware versions

Discovery Timeline

2025-10-22 - CVE-2025-41719 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-41719

Vulnerability Analysis

The flaw resides in the webserver component responsible for storing and managing user accounts on the device. When a low-privileged authenticated user submits user-related input containing characters the storage layer does not support, the parser fails to reject the request safely. Instead of returning a validation error, the webserver corrupts the underlying user database. The corruption triggers a recovery path that wipes the existing account list and provisions a built-in Administrator account using factory-default credentials. An attacker who knows the default password — typically published in vendor documentation — then logs in with full administrative privileges. This combines an input validation defect with an insecure recovery routine, producing a complete authentication bypass for any remote attacker who already holds minimal access.

Root Cause

The root cause is improper validation of the syntactic correctness of input written to the user storage backend [CWE-1286]. The webserver accepts character sequences outside the expected grammar of the user record format. Persisting these sequences breaks the storage structure, and the device's self-healing logic responds by reinitializing the account database to a known-default state rather than rejecting the malformed write.

Attack Vector

Exploitation requires network access to the webserver and a low-privileged authenticated session. The attacker submits a crafted request containing unsupported characters to a user-management endpoint. After the storage corruption is triggered, the attacker authenticates as the recreated default Administrator using the vendor's documented default password. No user interaction is required.

No verified public proof-of-concept code is available. Technical details are documented in the CERT VDE CSAF advisory.

Detection Methods for CVE-2025-41719

Indicators of Compromise

Unexpected disappearance of configured user accounts from the device's user list
Presence of the factory-default Administrator account on a device that previously had it disabled or removed
Successful logins using the vendor's documented default Administrator credentials
Webserver requests to user-management endpoints containing non-printable or non-ASCII byte sequences

Detection Strategies

Inspect webserver access logs for POST or PUT requests to user-administration endpoints originating from low-privileged accounts
Alert when authentication events show the default Administrator account being used, especially from external network ranges
Baseline the configured user list and trigger alerts on unexplained mass-deletion events

Monitoring Recommendations

Forward device webserver and authentication logs to a centralized SIEM for correlation
Monitor configuration-change events on operational technology and building-automation devices that expose web interfaces
Track failed input-validation errors emitted by the webserver to identify probing activity preceding exploitation

How to Mitigate CVE-2025-41719

Immediate Actions Required

Apply the firmware update referenced in the CERT VDE advisory vde-2025-060 as soon as it is available for your device model
Change the default Administrator password on all affected devices and verify the default account is disabled where supported
Restrict network access to the device webserver to trusted management networks only
Audit existing low-privileged accounts and remove any that are unnecessary

Patch Information

Refer to the vendor advisory published through CERT VDE for fixed firmware versions and update procedures. The advisory is available at sauter.csaf-tp.certvde.com. Devices should be updated to the firmware release identified in the CSAF document for the specific product line.

Workarounds

Place affected devices behind a network firewall and permit webserver access only from a dedicated management VLAN
Disable remote webserver access where operational requirements allow, using local console administration instead
Enforce strong, unique credentials and immediately rotate the default Administrator password after any device reset
Monitor for account-list changes and alert administrators to any reappearance of the default Administrator user

bash

# Example: restrict webserver access to a management subnet using iptables on an upstream gateway
iptables -A FORWARD -p tcp -s 10.10.20.0/24 -d <device_ip> --dport 443 -j ACCEPT
iptables -A FORWARD -p tcp -d <device_ip> --dport 443 -j DROP