CVE-2012-5533 in lighttpd
Summary
by MITRE
The http_request_split_value function in request.c in lighttpd before 1.4.32 allows remote attackers to cause a denial of service (infinite loop) via a request with a header containing an empty token, as demonstrated using the "Connection: TE,,Keep-Alive" header.
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Analysis
by VulDB Data Team • 12/29/2024
The vulnerability identified as CVE-2012-5533 affects lighttpd web servers version 1.4.31 and earlier, representing a critical denial of service flaw that can be exploited by remote attackers to disrupt service availability. This issue stems from improper handling of HTTP header parsing within the http_request_split_value function located in the request.c source file, which processes incoming HTTP requests and extracts header values for further processing. The vulnerability specifically manifests when the web server encounters HTTP headers containing empty tokens, creating a condition that leads to an infinite loop during request processing. The attack vector is demonstrated through a carefully crafted header value such as "Connection: TE,,Keep-Alive" where the double comma creates an empty token that the parser cannot properly handle, causing the server to enter a continuous loop while attempting to process the malformed header.
The technical implementation of this vulnerability involves the parsing logic that splits HTTP header values based on delimiter characters such as commas, without proper validation of empty tokens in the resulting split array. When the http_request_split_value function encounters an empty token, it fails to recognize this as an invalid state and continues processing, leading to an infinite loop that consumes CPU resources indefinitely. This behavior is classified as a denial of service condition under CWE-400, specifically related to uncontrolled resource consumption where the server's processing capabilities are exhausted through malformed input. The vulnerability represents a classic example of insufficient input validation and error handling in network protocol parsing, where the absence of proper bounds checking and token validation allows malformed data to trigger unintended program behavior.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise server availability and resource allocation within production environments. An attacker can exploit this weakness by sending a single malicious HTTP request containing the specially crafted header, causing the lighttpd process to consume excessive CPU cycles until the system resources are exhausted or the process is manually terminated. This type of attack can be particularly devastating in high-traffic environments where multiple concurrent connections are handled, as the infinite loop affects the server's ability to process legitimate requests, effectively creating a denial of service condition that impacts all users. The vulnerability demonstrates the critical importance of robust input validation in network services, as even seemingly benign malformed headers can cause significant operational disruption.
Mitigation strategies for CVE-2012-5533 focus primarily on upgrading to lighttpd version 1.4.32 or later, where the parsing logic has been corrected to properly handle empty tokens in HTTP headers. System administrators should implement immediate patch management procedures to update affected servers and verify that the fix has been properly applied. Additional protective measures include implementing web application firewalls or intrusion prevention systems that can detect and block malformed HTTP headers before they reach the web server. Network-level protections such as rate limiting and connection throttling can help reduce the impact of such attacks by limiting the number of requests that can be processed from a single source within a given timeframe. The vulnerability also highlights the need for comprehensive security testing of network protocol implementations, particularly focusing on edge cases and malformed input handling as recommended by the ATT&CK framework's network protocol manipulation techniques. Organizations should also consider implementing monitoring and alerting mechanisms to detect unusual CPU utilization patterns that may indicate exploitation of this or similar vulnerabilities.