CVE-2005-4348 in Fetchmail
Summary
by MITRE
fetchmail before 6.3.1 and before 6.2.5.5, when configured for multidrop mode, allows remote attackers to cause a denial of service (application crash) by sending messages without headers from upstream mail servers.
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Analysis
by VulDB Data Team • 06/13/2019
The vulnerability described in CVE-2005-4348 represents a critical denial of service weakness in fetchmail versions prior to 6.3.1 and 6.2.5.5 when operating in multidrop mode configuration. This flaw specifically targets the mail retrieval utility that functions as a mail forwarder and reader, commonly used in enterprise environments to aggregate mail from multiple sources. The vulnerability stems from insufficient input validation mechanisms within the fetchmail application when processing incoming messages that lack proper header information.
The technical implementation of this vulnerability occurs during the message parsing phase of fetchmail's multidrop functionality, where the application fails to properly handle messages that are missing essential header fields. When upstream mail servers transmit emails without complete header information, fetchmail's parsing routines encounter unexpected data structures that cause the application to crash or terminate unexpectedly. This occurs because the software does not implement robust error handling for malformed message formats, particularly in the context of multidrop configurations where multiple recipients are processed simultaneously. The vulnerability is particularly dangerous as it can be exploited remotely through simple message transmission without requiring authentication or privileged access.
The operational impact of this vulnerability extends beyond simple service disruption, as fetchmail instances running in production environments may experience repeated crashes when processing legitimate but malformed messages from external sources. In multidrop configurations, where fetchmail acts as a central mail processing hub for multiple users or systems, a single malicious or misconfigured upstream server can bring down the entire mail processing infrastructure. Network administrators face the challenge of maintaining mail service availability while dealing with unpredictable application crashes that can occur at any time. The vulnerability also exposes potential for cascading failures in larger network architectures where fetchmail serves as a critical component in email routing and distribution systems.
Organizations should immediately implement patch management procedures to upgrade fetchmail installations to versions 6.3.1 or 6.2.5.5 or later, which contain the necessary fixes for header validation and error handling. System administrators should also consider implementing additional monitoring and alerting mechanisms to detect application crashes and automatically restart fetchmail services. Network segmentation strategies can help limit the impact of such vulnerabilities by isolating fetchmail instances from critical infrastructure components. This vulnerability aligns with CWE-129, which addresses improper validation of input, and corresponds to attack patterns found in the MITRE ATT&CK framework under initial access and execution phases where adversaries leverage service disruption techniques. Organizations should also review their email infrastructure configurations to ensure proper validation of incoming messages and implement redundant mail processing systems to maintain service availability during potential exploitation attempts.