CVE-2025-2595: CODESYS Auth Bypass Vulnerability

CVE-2025-2595 Overview

CVE-2025-2595 is an information disclosure vulnerability in CODESYS Visualization. An unauthenticated remote attacker can bypass the user management controls and read visualization template files or static elements through forced browsing. The flaw is categorized under [CWE-425: Direct Request (Forced Browsing)], where the application relies on the assumption that clients will only access resources through expected navigation paths.

Critical Impact
Remote unauthenticated attackers can retrieve protected visualization templates and static assets from CODESYS Visualization deployments, exposing operational technology (OT) design details without any authentication.

Affected Products

CODESYS Visualization
CODESYS TargetVisu components exposing visualization content over the network
Deployments integrating CODESYS Visualization user management for access control

Discovery Timeline

2025-04-23 - CVE-2025-2595 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-2595

Vulnerability Analysis

CODESYS Visualization enforces user management to restrict access to templates and static visualization elements. The vulnerability exists because the server does not consistently validate authentication when clients request resource URLs directly. An attacker who guesses or enumerates the resource paths can download visualization templates and static content without ever authenticating.

The confidentiality impact is limited to information already stored as visualization content, but that content frequently reveals HMI layout, tag names, control logic references, and operator workflows. Integrity and availability are not affected. Exploitation requires only network reachability to the visualization service.

This class of weakness, forced browsing, occurs when authorization checks are enforced only at the navigation layer rather than at the resource layer. Attackers rely on predictable file names or directory structures to bypass menu-driven access controls.

Root Cause

The root cause is missing authorization enforcement on direct resource requests. User management gates the primary visualization interface, but static assets and template files are served without re-checking session state or credentials. See the CERT-VDE Security Advisory for vendor details.

Attack Vector

Exploitation requires an HTTP request to the exposed CODESYS Visualization endpoint with a resource path that maps to a template or static element. No credentials, user interaction, or elevated privileges are required. The attacker only needs network reachability to the target service.

No verified public exploit code is available for this issue. Refer to the vendor advisory for technical specifics and affected version ranges.

Detection Methods for CVE-2025-2595

Indicators of Compromise

Unauthenticated HTTP GET requests to CODESYS Visualization template or static asset paths from external or unexpected source IP addresses.
Sequential or dictionary-style requests against visualization resource directories indicating enumeration.
Access log entries showing successful responses (HTTP 200) for template files without a preceding authentication event.

Detection Strategies

Inspect web server or reverse proxy logs in front of CODESYS Visualization services for direct requests to .tmpl, image, or static resource paths without a prior authenticated session.
Deploy network intrusion detection signatures that flag anomalous request patterns targeting known CODESYS Visualization URIs.
Correlate OT network flow data with expected HMI client IPs to surface unauthorized clients touching visualization endpoints.

Monitoring Recommendations

Enable verbose access logging on the CODESYS Visualization web listener and forward logs to a centralized SIEM for retention and correlation.
Alert on any external source addresses reaching visualization services that should be constrained to engineering or operator subnets.
Baseline normal request rates per client and alert on spikes consistent with forced-browsing enumeration.

How to Mitigate CVE-2025-2595

Immediate Actions Required

Apply the CODESYS patch referenced in the CERT-VDE Security Advisory VDE-2025-027 as soon as it is available for your product version.
Restrict network access to CODESYS Visualization services so only authorized engineering workstations and HMI clients can reach them.
Audit visualization content to identify any templates or static assets that would disclose sensitive process information if exposed.

Patch Information

CODESYS and CERT-VDE have coordinated a fix for this issue. Consult the CERT-VDE Security Advisory for the list of fixed versions and download locations. Apply updates during scheduled maintenance windows following standard OT change management procedures.

Workarounds

Place CODESYS Visualization endpoints behind a VPN or jump host and block direct exposure to untrusted networks.
Enforce network segmentation between IT and OT zones using firewalls that allow visualization traffic only from designated client ranges.
Where feasible, front the visualization service with a reverse proxy that enforces authentication before requests reach the upstream server.

bash

# Configuration example: restrict CODESYS Visualization access with iptables
iptables -A INPUT -p tcp --dport 8080 -s 10.10.20.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP