CVE-2008-0983 in lighttpd
Summary
by MITRE
lighttpd 1.4.18, and possibly other versions before 1.5.0, does not properly calculate the size of a file descriptor array, which allows remote attackers to cause a denial of service (crash) via a large number of connections, which triggers an out-of-bounds access.
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Analysis
by VulDB Data Team • 08/06/2019
The vulnerability identified as CVE-2008-0983 affects lighttpd web server versions 1.4.18 and earlier, with potential impacts extending to versions prior to 1.5.0. This issue represents a critical memory management flaw that fundamentally undermines the server's ability to handle concurrent network connections. The vulnerability resides in the server's file descriptor array calculation mechanism, where the system fails to properly account for the maximum number of connections that can be simultaneously processed, creating a scenario where legitimate connection handling becomes impossible.
The technical root cause of this vulnerability stems from improper buffer size calculation within the server's connection handling subsystem. When lighttpd receives a large number of concurrent connections, the software attempts to allocate and manage file descriptor arrays based on flawed mathematical calculations or assumptions about connection limits. This miscalculation results in the system attempting to access memory locations beyond the allocated array boundaries, triggering an out-of-bounds memory access condition. Such memory corruption typically manifests as a segmentation fault or similar memory access violation that causes the web server process to terminate unexpectedly, leading to complete service disruption for all connected clients.
The operational impact of this vulnerability extends beyond simple service interruption to encompass significant security and availability concerns. Remote attackers can exploit this weakness by establishing a large number of concurrent connections to the target lighttpd server, effectively overwhelming the system's ability to manage these connections properly. The resulting denial of service condition can be particularly devastating in production environments where web servers handle critical business traffic, potentially causing financial losses, service degradation, or complete unavailability of web applications. This vulnerability aligns with CWE-129, which addresses improper validation of array indices, and represents a classic example of a buffer overflow condition that can be exploited for denial of service attacks.
From an attack methodology perspective, this vulnerability demonstrates how seemingly benign connection handling operations can be weaponized to cause system instability. The exploit requires minimal sophistication since it only necessitates establishing multiple connections to the target server, making it particularly dangerous as it can be executed by attackers with limited technical expertise. The vulnerability's impact is amplified by the fact that it affects the core server functionality, meaning that even a single successful exploitation attempt can completely disable the web server service. Organizations should consider this issue in relation to ATT&CK technique T1499.004, which covers network denial of service attacks targeting web servers, and recognize the importance of implementing proper input validation and resource management controls.
The recommended mitigation strategy involves immediate deployment of lighttpd version 1.5.0 or later, which contains the necessary fixes to properly calculate file descriptor array sizes and prevent out-of-bounds memory access. Additionally, system administrators should implement connection rate limiting mechanisms and monitor for unusual connection patterns that might indicate exploitation attempts. Network-level protections such as firewall rules that limit concurrent connections from individual IP addresses can provide additional defense-in-depth measures. Organizations should also consider implementing intrusion detection systems that can identify patterns consistent with this type of denial of service attack and establish proper logging and monitoring to detect potential exploitation attempts. The fix addresses the underlying memory management issue while maintaining backward compatibility and ensuring that legitimate connection handling operations proceed without disruption.