CVE-2026-11833 Overview
CVE-2026-11833 is an information disclosure vulnerability affecting Yokogawa FAST/TOOLS and CI Server. The web server returns responses containing CI Server configuration information to unauthenticated network clients. An attacker can collect this configuration data and use it to plan follow-on attacks against the industrial control environment.
The issue is tracked under CWE-319 (Cleartext Transmission of Sensitive Information) and is documented in Yokogawa Security Advisory YSAR-26-0004.
Critical Impact
Remote, unauthenticated attackers can retrieve CI Server settings over the network, enabling reconnaissance against industrial control systems used in process automation environments.
Affected Products
- FAST/TOOLS packages RVSVRN, UNSVRN, HMIWEB, FTEES, and HMIMOB, versions R9.01 through R10.04
- CI Server, all packages, versions R1.01 through R1.04
- Yokogawa industrial control deployments exposing the affected web server
Discovery Timeline
- 2026-06-23 - CVE-2026-11833 published to NVD
- 2026-06-23 - Last updated in NVD database
- 2026-06-25 - EPSS scoring data published
Technical Details for CVE-2026-11833
Vulnerability Analysis
The FAST/TOOLS and CI Server web server exposes internal configuration information in HTTP responses. The exposed data describes CI Server settings that should remain confidential within the operational technology environment. Because the response is returned over the network without authentication, any attacker who can reach the web service can collect this data.
The vulnerability is classified under [CWE-319], which covers the transmission of sensitive information without adequate protection. The disclosed settings can reveal architectural details, software components, and operational parameters of the industrial control deployment. Attackers commonly use this kind of reconnaissance to identify additional weaknesses, craft targeted exploits, and pivot deeper into supervisory and control networks.
Root Cause
The web server bundled with FAST/TOOLS and CI Server includes CI Server setting information in responses that should not return that data. The server fails to restrict or sanitize configuration content before returning it to remote clients. No authentication or authorization control gates the exposed endpoint.
Attack Vector
An attacker reaches the affected web server over the network and issues a request that triggers the disclosing response. The attack requires no privileges and no user interaction. The CVSS 4.0 vector indicates that exploitation depends on a passive attack condition but does not require credentials or social engineering.
The vulnerability impacts confidentiality only. Integrity and availability of the FAST/TOOLS and CI Server systems are not directly affected by this issue. However, the disclosed information can support subsequent attacks that do affect integrity and availability.
No public proof-of-concept exploit has been published, and the issue is not listed in the CISA Known Exploited Vulnerabilities catalog.
Detection Methods for CVE-2026-11833
Indicators of Compromise
- Unexpected HTTP requests to FAST/TOOLS or CI Server web endpoints originating from systems outside normal engineering workstations
- Outbound traffic patterns showing CI Server configuration strings or setting identifiers in HTTP responses
- Repeated probing of the web server from a single source address over short time windows
Detection Strategies
- Inspect HTTP response bodies returned by FAST/TOOLS and CI Server hosts for configuration fields that should not leave the OT network
- Correlate web server access logs with asset inventories to identify requests from unauthorized clients
- Apply network intrusion detection signatures that flag access to the affected web server from non-engineering subnets
Monitoring Recommendations
- Forward FAST/TOOLS and CI Server web server logs to a centralized log platform for retention and analysis
- Alert on any external or DMZ-originated traffic reaching FAST/TOOLS and CI Server TCP ports
- Baseline normal web server response sizes and content types, then alert on responses that deviate from that baseline
How to Mitigate CVE-2026-11833
Immediate Actions Required
- Identify all FAST/TOOLS instances running R9.01 through R10.04 and CI Server instances running R1.01 through R1.04
- Restrict network access to the affected web server so that only authorized engineering workstations can reach it
- Contact Yokogawa support to obtain the fixed package versions and apply them following vendor change-control guidance
- Review web server logs for evidence of unauthorized requests prior to remediation
Patch Information
Yokogawa provides remediation guidance in Yokogawa Security Advisory YSAR-26-0004. Operators should consult the advisory for the specific FAST/TOOLS and CI Server package updates and follow Yokogawa's recommended upgrade procedure for production OT systems.
Workarounds
- Place the FAST/TOOLS and CI Server web server behind a network segmentation boundary that blocks untrusted clients
- Enforce firewall rules that allow web access only from defined engineering workstation IP ranges
- Disable the affected web service on systems where it is not required for daily operations
- Require VPN or jump-host access for any operator who needs to reach the FAST/TOOLS or CI Server web interface remotely
# Example firewall restriction limiting access to the FAST/TOOLS web server
# Replace interface, source range, and destination IP with site-specific values
iptables -A INPUT -p tcp --dport 443 -s 10.10.20.0/24 -d 10.10.50.10 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -d 10.10.50.10 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
