CVE-2025-67445 in X5000R
Summary
by MITRE • 02/24/2026
TOTOLINK X5000R V9.1.0cu.2415_B20250515 contains a denial-of-service vulnerability in /cgi-bin/cstecgi.cgi. The CGI reads the CONTENT_LENGTH environment variable and allocates memory using malloc (CONTENT_LENGTH + 1) without sufficient bounds checking. When lighttpd s request size limit is not enforced, a crafted large POST request can cause memory exhaustion or a segmentation fault, leading to a crash of the management CGI and loss of availability of the web interface.
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Analysis
by VulDB Data Team • 02/28/2026
The vulnerability identified as CVE-2025-67445 affects the TOTOLINK X5000R router firmware version V9.1.0cu.2415_B20250515 and resides within the /cgi-bin/cstecgi.cgi component. This represents a classic buffer overflow scenario where the application fails to properly validate input parameters before processing them. The specific flaw manifests in how the Common Gateway Interface handles the CONTENT_LENGTH environment variable, which is typically used to indicate the size of incoming request data. When this variable is improperly trusted and used directly for memory allocation without adequate bounds validation, it creates a pathway for malicious input to cause unintended behavior.
The technical implementation of this vulnerability stems from the application's memory management practices where malloc is called with a size parameter derived directly from CONTENT_LENGTH plus one byte. This approach assumes that the CONTENT_LENGTH value is trustworthy and within reasonable bounds, which is not the case in practice. The absence of proper input validation means that an attacker can craft a POST request with an extraordinarily large CONTENT_LENGTH value, causing the application to attempt to allocate an excessive amount of memory. This memory allocation failure can manifest as either a segmentation fault or complete memory exhaustion, depending on the system's response to the allocation attempt.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire network management interface of the affected device. When the lighttpd web server processes the malicious request, it crashes the management CGI component, rendering the web-based administration interface inaccessible. This denial-of-service condition affects legitimate users who require access to configure their router settings, potentially leaving them unable to manage network parameters, update firmware, or monitor security settings. The vulnerability is particularly concerning because it targets the administrative interface that network administrators rely upon for device management, effectively cutting off authorized access to critical network configuration capabilities.
This vulnerability aligns with CWE-122 (Heap-based Buffer Overflow) and CWE-787 (Out-of-bounds Write) in the Common Weakness Enumeration catalog, demonstrating poor input validation and memory management practices. From an adversarial perspective, this flaw maps to ATT&CK technique T1499.004 (Endpoint Denial of Service) and potentially T1566.001 (Phishing via Social Engineering) when combined with other attack vectors. The vulnerability's exploitation requires minimal sophistication and can be automated, making it attractive to threat actors seeking to disrupt network services. Organizations should consider implementing network segmentation to limit exposure, as well as monitoring for unusual traffic patterns that might indicate exploitation attempts, particularly around the affected CGI endpoint. The recommended mitigation involves firmware updates from the vendor that implement proper bounds checking on the CONTENT_LENGTH variable and enforce reasonable limits on request sizes to prevent excessive memory allocation attempts.