CVE-2007-1869 in lighttpd
Summary
by MITRE
lighttpd 1.4.12 and 1.4.13 allows remote attackers to cause a denial of service (cpu and resource consumption) by disconnecting while lighttpd is parsing CRLF sequences, which triggers an infinite loop and file descriptor consumption.
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Analysis
by VulDB Data Team • 03/15/2021
The vulnerability described in CVE-2007-1869 represents a critical denial of service flaw affecting lighttpd web servers version 1.4.12 and 1.4.13. This issue stems from improper handling of HTTP request parsing logic where the server fails to properly validate connection states during CRLF sequence processing. The flaw manifests when remote attackers intentionally disconnect during the parsing phase, creating a condition that leads to resource exhaustion and system instability.
The technical root cause of this vulnerability lies in the server's inability to gracefully handle abrupt client disconnections during HTTP request processing. When lighttpd encounters a client that disconnects while the server is in the process of parsing CRLF (Carriage Return Line Feed) sequences, the parsing logic enters an infinite loop. This occurs because the server's state machine does not properly account for the possibility of client disconnection during parsing operations, causing the server to continuously attempt to process incomplete data structures. The infinite loop consumes excessive CPU cycles while simultaneously maintaining file descriptor references, leading to progressive resource depletion.
From an operational perspective, this vulnerability presents a significant threat to web server availability and system stability. Attackers can exploit this flaw by establishing connections to the lighttpd server and then immediately disconnecting without completing the HTTP request process. The server's response to such disconnections results in sustained high CPU utilization and gradual file descriptor exhaustion, ultimately causing legitimate service requests to fail and potentially leading to complete service unavailability. The impact extends beyond simple resource consumption as the infinite loop can cause the server to become unresponsive to all incoming requests.
This vulnerability aligns with CWE-400, which addresses "Uncontrolled Resource Consumption" and specifically relates to improper handling of resource cleanup during abnormal termination conditions. The flaw also demonstrates characteristics consistent with ATT&CK technique T1499.004, "Endpoint Denial of Service," where adversaries leverage software weaknesses to consume system resources and cause service disruption. The issue particularly affects web servers that must maintain high availability and handle concurrent connections, making it especially dangerous in production environments where service continuity is critical.
The recommended mitigation strategy involves upgrading to lighttpd version 1.4.14 or later, where the parsing logic has been corrected to properly handle client disconnections during CRLF sequence processing. Administrators should also implement connection timeout configurations and monitor for unusual CPU usage patterns that might indicate exploitation attempts. Network-level protections such as rate limiting and connection tracking can provide additional defense-in-depth measures, while regular security audits should verify that all web server components are running patched versions to prevent similar vulnerabilities from compromising system availability.