CVE-2016-9564 in Webserver
Summary
by MITRE
Buffer overflow in send_redirect() in Boa Webserver 0.92r allows remote attackers to DoS via an HTTP GET request requesting a long URI with only '/' and '.' characters.
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Analysis
by VulDB Data Team • 06/13/2019
The vulnerability identified as CVE-2016-9564 represents a critical buffer overflow condition within the Boa Webserver version 0.92r implementation. This flaw exists in the send_redirect() function which handles HTTP redirect responses, creating a pathway for remote attackers to exploit the web server through carefully crafted HTTP GET requests. The specific trigger involves requests that contain excessively long URIs composed solely of forward slash and period characters, which the server fails to properly validate or limit during processing.
The technical mechanism behind this vulnerability stems from inadequate input validation within the web server's URI handling logic. When Boa Webserver processes an HTTP GET request with an abnormally long URI consisting primarily of '/' and '.' characters, the send_redirect() function does not properly bounds-check the incoming data before copying it into fixed-size buffers. This classic buffer overflow scenario occurs because the server allocates memory for URI processing without sufficient validation of the input length, allowing attackers to exceed the allocated buffer boundaries and overwrite adjacent memory regions.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a potential pathway for more sophisticated attacks. Remote attackers can leverage this flaw to crash the web server process, causing legitimate users to lose access to web services hosted on the affected server. The vulnerability's exploitation requires minimal complexity since attackers only need to construct a specific URI pattern rather than employing complex attack vectors. This makes the vulnerability particularly dangerous as it can be triggered by automated scanning tools or simple web crawlers that might inadvertently construct such malformed requests during normal browsing activities.
From a cybersecurity perspective, this vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a clear example of improper input validation in network services. The attack pattern follows typical remote code execution or denial of service methodologies documented in the MITRE ATT&CK framework under the T1499 category for network denial of service attacks. The flaw demonstrates the importance of implementing robust input validation and bounds checking in all network-facing applications, particularly those handling user-supplied data such as HTTP URIs.
The mitigation strategies for this vulnerability require immediate attention from system administrators and security teams. The most effective solution involves applying the vendor-provided patch or upgrading to a newer version of the Boa Webserver that addresses this buffer overflow condition. Organizations should also implement network-level protections such as web application firewalls that can detect and block suspicious URI patterns before they reach the vulnerable server. Additionally, implementing proper input length validation and memory bounds checking in custom web server configurations can provide defense-in-depth protection against similar vulnerabilities. Regular security assessments and penetration testing should include verification of buffer overflow conditions in all network services to prevent exploitation of similar weaknesses that may exist in other components of the web infrastructure stack.