CVE-2023-23581 in VPN
Summary
by MITRE • 10/25/2023
A denial-of-service vulnerability exists in the vpnserver EnSafeHttpHeaderValueStr functionality of SoftEther VPN 5.01.9674 and 5.02. A specially crafted network packet can lead to denial of service.
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Analysis
by VulDB Data Team • 10/25/2023
The vulnerability identified as CVE-2023-23581 represents a critical denial-of-service weakness within the SoftEther VPN software ecosystem, specifically affecting versions 5.01.9674 and 5.02 of the vpnserver component. This issue manifests within the EnSafeHttpHeaderValueStr functionality, which processes HTTP header values during network communication. The vulnerability arises from insufficient input validation mechanisms that fail to properly sanitize or reject malformed network packets. Attackers can exploit this weakness by crafting specifically designed packets that trigger unexpected behavior in the vpnserver application, ultimately leading to service disruption and complete denial of access for legitimate users. The affected SoftEther VPN implementation processes HTTP headers without adequate boundary checks or data sanitization, creating an entry point for malicious actors to compromise system availability.
The technical flaw resides in the improper handling of HTTP header values within the EnSafeHttpHeaderValueStr function, which operates as part of the HTTP protocol processing layer in SoftEther VPN server implementations. This function lacks proper validation routines to detect and reject malformed or oversized header data that could cause memory corruption or resource exhaustion. When processing network traffic, the system fails to implement bounds checking or input sanitization mechanisms that would normally prevent such vulnerabilities. The vulnerability class aligns with CWE-129, Input Validation, and CWE-772, Missing Release of Resource, as the improper handling of input data can lead to resource exhaustion or memory corruption. The flaw operates at the application layer of the network stack, making it particularly dangerous as it can be exploited through standard network protocols without requiring specialized access or privileges.
The operational impact of CVE-2023-23581 extends beyond simple service interruption to potentially compromise entire network infrastructure that relies on SoftEther VPN for secure communications. Organizations utilizing affected versions may experience complete service outages, particularly in environments where VPN connectivity is critical for remote access, business continuity, or secure data transmission. The vulnerability can be exploited remotely, meaning attackers need only send malicious packets to the target system without requiring physical access or authentication credentials. This characteristic makes the vulnerability particularly attractive to threat actors seeking to disrupt operations or create chaos within network environments. The attack vector primarily targets the HTTP processing components of the vpnserver, making it effective against systems that utilize HTTP-based protocols for VPN management or authentication services, potentially affecting thousands of installations worldwide.
Mitigation strategies for CVE-2023-23581 should prioritize immediate software updates to versions that contain patches addressing the input validation weaknesses in the EnSafeHttpHeaderValueStr functionality. Organizations should implement network segmentation and access controls to limit exposure of vulnerable vpnserver instances to untrusted networks, while also deploying intrusion detection systems that can identify suspicious HTTP header patterns. The implementation of rate limiting and connection throttling mechanisms can help reduce the impact of potential denial-of-service attempts by limiting the number of requests that can be processed within a given timeframe. Additionally, organizations should consider deploying web application firewalls or network security appliances that can filter out malformed HTTP headers before they reach the vulnerable vpnserver components. According to ATT&CK framework category T1499, Network Denial of Service, and T1595, Active Scanning, this vulnerability represents a significant threat that requires both preventive measures and monitoring capabilities to detect and respond to exploitation attempts effectively.