CVE-2021-34586 in V2 Web Server
Summary
by MITRE • 10/26/2021
In the CODESYS V2 web server prior to V1.1.9.22 crafted web server requests may cause a Null pointer dereference in the CODESYS web server and may result in a denial-of-service condition.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 08/15/2025
The vulnerability identified as CVE-2021-34586 affects the CODESYS V2 web server software, specifically targeting versions prior to V1.1.9.22. This issue represents a critical security flaw that arises from improper input validation within the web server component of the CODESYS runtime environment. The affected system operates as a web server interface for industrial automation and control systems, making it a potential target for attackers seeking to disrupt operational technology infrastructure. The vulnerability manifests when maliciously crafted web server requests are processed by the affected software, creating a condition where the application attempts to dereference a null pointer during request handling. This type of flaw falls under the category of improper input validation and memory management issues that are commonly exploited in denial-of-service attacks against industrial control systems. The impact extends beyond simple service disruption as it can affect the reliability of critical industrial processes that depend on CODESYS for automation and control functions.
The technical root cause of this vulnerability stems from a null pointer dereference condition that occurs within the web server's request processing logic. When the web server receives specially crafted HTTP requests, the application fails to properly validate or handle certain request parameters, leading to a scenario where a pointer variable that should contain a valid memory address instead holds a null value. During subsequent processing operations, the software attempts to access this null pointer, causing an application crash or termination. This behavior aligns with CWE-476, which specifically addresses null pointer dereference vulnerabilities, and represents a fundamental flaw in the software's defensive programming practices. The vulnerability is particularly concerning in industrial environments where continuous operation is critical, as the denial-of-service condition can result in unplanned system downtime and potential production losses.
The operational impact of CVE-2021-34586 extends significantly beyond traditional information technology environments into industrial control systems where CODESYS is commonly deployed. Organizations utilizing CODESYS for building automation, manufacturing control, and industrial process management face potential disruption of their operational technology infrastructure when this vulnerability is exploited. The denial-of-service condition can affect the availability of web-based interfaces used for system monitoring, configuration management, and remote access to industrial processes. Attackers can leverage this vulnerability to systematically disrupt operations by sending malicious requests that cause the web server to crash repeatedly, potentially leading to extended downtime periods. This vulnerability directly impacts the availability aspect of the CIA triad and can be classified under ATT&CK technique T1499.1, which focuses on network denial of service attacks targeting operational technology systems. The exploitation of this vulnerability can result in cascading effects throughout industrial networks where the web server serves as a critical interface point for system management and monitoring activities.
Organizations should immediately implement mitigations to address this vulnerability by upgrading to CODESYS V1.1.9.22 or later versions where the null pointer dereference issue has been resolved. The recommended approach involves conducting a comprehensive inventory of all systems running affected CODESYS web server versions and scheduling mandatory updates as part of routine maintenance procedures. Network segmentation and access control measures should be implemented to limit exposure of the affected web server components to untrusted networks or users. Additionally, organizations should deploy intrusion detection systems capable of identifying and blocking malicious web requests that exhibit characteristics associated with this vulnerability. Regular security assessments and penetration testing should be conducted to verify the effectiveness of implemented controls and identify potential additional vulnerabilities in industrial control system environments. The mitigation strategy should also include monitoring for unusual patterns of web server access or application crashes that may indicate exploitation attempts, as these systems often operate in environments where traditional IT security controls may not be fully implemented or effective.