CVE-2003-0744 in Leafnode
Summary
by MITRE
The fetchnews NNTP client in leafnode 1.9.3 to 1.9.41 allows remote attackers to cause a denial of service (process hang and termination) via certain malformed Usenet news articles that cause fetchnews to hang while waiting for input.
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Analysis
by VulDB Data Team • 06/07/2019
The vulnerability described in CVE-2003-0744 represents a critical denial of service flaw within the fetchnews NNTP client component of leafnode versions 1.9.3 through 1.9.41. This issue specifically targets the handling of malformed Usenet news articles that are processed through the Network News Transfer Protocol, creating a scenario where the fetchnews utility becomes unresponsive and eventually terminates. The vulnerability stems from inadequate input validation mechanisms within the NNTP client implementation, which fails to properly sanitize or reject malformed data streams that are commonly encountered in Usenet traffic.
The technical execution of this vulnerability occurs when an attacker crafts and distributes malformed Usenet news articles that exploit parsing inconsistencies in the fetchnews utility. These malformed articles contain specially constructed data sequences that cause the client to enter an infinite wait state while attempting to process input from the NNTP server. The flaw is particularly insidious because it operates at the protocol level, where the client expects structured data but receives unexpected or corrupted input that disrupts normal processing flow. This behavior creates a resource exhaustion scenario where system processes become blocked indefinitely, effectively rendering the fetchnews utility unusable for legitimate news article retrieval operations.
From an operational impact perspective, this vulnerability creates significant disruption for Usenet news server administrators and users who rely on leafnode for news article distribution and retrieval. The denial of service condition can persist for extended periods, potentially requiring manual intervention to restart the affected services or even system rebooting. The vulnerability affects the availability of news services, making legitimate users unable to access newsgroups or retrieve recent articles until the affected processes are manually terminated or system resources are freed. This impacts not only individual users but also broader Usenet infrastructure that depends on reliable NNTP client implementations for proper operation.
The vulnerability aligns with CWE-400, which categorizes improper input validation as a fundamental weakness in software design that can lead to denial of service conditions. This flaw also maps to ATT&CK technique T1499.004, which describes network denial of service attacks that target services through malformed inputs. The root cause demonstrates poor error handling and input sanitization practices that are commonly found in legacy network applications. Security practitioners should note that this vulnerability represents a classic example of how insufficient validation of external inputs can lead to process-level disruptions that compromise system availability.
Mitigation strategies for this vulnerability include immediate patching of leafnode installations to versions that address the input validation issues in fetchnews. System administrators should also implement network-level filtering to identify and block malformed NNTP traffic before it reaches vulnerable clients. Additional protective measures include configuring process timeouts and resource limits to prevent indefinite hanging conditions, implementing monitoring alerts for process starvation, and establishing redundant news retrieval mechanisms to maintain service availability during remediation periods. Regular security assessments of network services and input validation routines should be conducted to identify similar vulnerabilities in other legacy applications.