CVE-2025-15681 Overview
CVE-2025-15681 is an authentication bypass vulnerability in the TBEA TLogger V2.1.0.0B0.0.0.0 web server. After any prior authenticated session on the device, an unauthenticated attacker can access the /index.asp endpoint and reach protected functionality without providing credentials. This exposure allows the attacker to view or modify device configuration and stored data. Logging out from the bypassed state can also crash the web server, producing a denial-of-service condition. The weakness is classified as Missing Authentication for Critical Function [CWE-306] and is exploitable over the network without user interaction.
Critical Impact
Unauthenticated remote attackers can access protected TLogger V2 functionality, alter device configuration, and crash the web server.
Affected Products
- TBEA TLogger V2.1.0.0B0.0.0.0
Discovery Timeline
- 2026-08-10 - CVE-2025-15681 published to NVD
- 2026-08-12 - Last updated in NVD database
Technical Details for CVE-2025-15681
Vulnerability Analysis
The TLogger V2 web server enforces authentication only conditionally. Once a legitimate user has authenticated to the device at any prior point, the server treats subsequent requests to /index.asp as trusted. An attacker who reaches the device over the network can then request protected pages without submitting credentials. The bypass grants access to functionality that should require an active session, including views and controls tied to device configuration and telemetry data. A secondary defect compounds the issue: initiating a logout from the bypassed state can cause the web server process to crash, disrupting operator access to the device.
Root Cause
The root cause is Missing Authentication for Critical Function [CWE-306]. The /index.asp handler relies on residual authentication state rather than validating a per-request session token. Session lifecycle handling is also incomplete, which is why the logout path can terminate the web server rather than cleanly invalidating the session.
Attack Vector
The attack vector is network-based and requires no privileges or user interaction. An attacker with reachability to the TLogger V2 web interface, typically on an operational technology (OT) or plant network, sends HTTP requests directly to /index.asp after any earlier authenticated session has occurred on the device. The attacker inherits access to protected endpoints and can read or change device parameters. Triggering a logout after abusing the bypass can crash the web server. TBEA is a Chinese manufacturer of transformer and power equipment, and TLogger devices are deployed in electrical monitoring environments, per the TBEA company overview.
No verified proof-of-concept code is publicly available. See the vendor references for technical details.
Detection Methods for CVE-2025-15681
Indicators of Compromise
- Requests to /index.asp on TLogger V2 devices originating from hosts that never completed an authentication exchange with the device.
- Configuration changes on TLogger V2 devices without a corresponding operator login in device logs.
- Unexpected TLogger V2 web server crashes or restarts correlating with HTTP logout requests.
Detection Strategies
- Monitor HTTP access logs on TLogger V2 devices for /index.asp requests lacking a preceding successful authentication for the same source address.
- Alert on any HTTP access to the TLogger V2 web interface from sources outside the approved OT engineering workstation range.
- Correlate device configuration write events with authenticated session identifiers to identify writes without a bound session.
Monitoring Recommendations
- Forward TLogger V2 web server logs, network flows, and OT firewall events to a centralized data lake for cross-source correlation.
- Baseline normal operator access patterns to TLogger V2 and alert on deviations in source IP, time of day, or request volume.
- Track TLogger V2 process availability and generate alerts when the embedded web server terminates unexpectedly.
How to Mitigate CVE-2025-15681
Immediate Actions Required
- Restrict network reachability to the TLogger V2 web interface using firewall rules that permit only designated engineering workstations.
- Place TLogger V2 devices behind a jump host or VPN so the web server is not directly exposed to general enterprise or field networks.
- Audit device configuration and stored data for unauthorized changes and reset device credentials.
Patch Information
No vendor advisory or firmware patch for CVE-2025-15681 is referenced in the NVD entry at time of publication. Operators should contact TBEA directly to confirm remediation status for TLogger V2.1.0.0B0.0.0.0 and monitor the TBEA vendor site for firmware updates.
Workarounds
- Segment TLogger V2 devices onto an isolated OT VLAN with explicit deny rules for all non-operator sources.
- Terminate lingering authenticated sessions by power-cycling or restarting the device after each legitimate operator use, until a firmware fix is available.
- Disable the web management interface on TLogger V2 units that are managed exclusively through out-of-band methods.
# Example: restrict TLogger V2 web access to a single engineering workstation
iptables -A FORWARD -s 10.10.20.15/32 -d 10.20.30.40/32 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d 10.20.30.40/32 -p tcp --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
