CVE-2006-5877 in enigmail
Summary
by MITRE
The enigmail extension before 0.94.2 does not properly handle large, encrypted file e-mail attachments, which allows remote attackers to cause a denial of service (crash), as demonstrated with Mozilla Thunderbird.
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Analysis
by VulDB Data Team • 07/30/2019
The vulnerability identified as CVE-2006-5877 affects the enigmail email encryption extension for Mozilla Thunderbird, specifically versions prior to 0.94.2. This flaw represents a significant security concern within email encryption systems where the extension fails to properly manage large encrypted file attachments, creating a potential vector for denial of service attacks. The issue manifests when the extension processes encrypted email attachments that exceed certain size thresholds, leading to application instability and potential crashes.
The technical root cause of this vulnerability lies in the improper handling of memory allocation and processing within the enigmail extension's attachment parsing routines. When large encrypted files are received as email attachments, the extension does not adequately validate or manage the memory resources required for decryption and processing. This deficiency creates a scenario where malicious actors can craft specially formatted encrypted attachments that trigger buffer overflow conditions or memory exhaustion errors within the Thunderbird email client. The vulnerability specifically targets the cryptographic processing pipeline where encrypted data is decrypted and prepared for display or attachment handling.
From an operational perspective, this vulnerability presents a substantial risk to email security infrastructure as it allows remote attackers to disrupt email services without requiring authentication or privileged access. The denial of service impact extends beyond individual user experiences to potentially affect entire email systems, particularly in environments where automated email processing or critical communication channels depend on Thunderbird clients. The attack vector is particularly concerning because it can be executed through standard email communication channels without requiring specialized tools or access to the target system. This makes the vulnerability exploitable in a wide range of scenarios from individual phishing attempts to large-scale service disruption campaigns.
The security implications of CVE-2006-5877 align with CWE-129, which addresses improper validation of input ranges, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. The vulnerability demonstrates how cryptographic extensions can introduce unexpected failure points in email clients, highlighting the importance of robust input validation and resource management in security tools. Organizations relying on email encryption systems must consider the potential for such failures to disrupt critical communication channels, particularly in mission-critical environments where email availability is paramount.
Mitigation strategies should prioritize immediate patching of the enigmail extension to version 0.94.2 or later, which contains the necessary fixes for proper large file handling. System administrators should also implement monitoring for unusual email traffic patterns that might indicate exploitation attempts, particularly around large attachment processing. Additional protective measures include configuring email client security policies to limit attachment sizes, implementing email filtering rules to detect and quarantine suspicious encrypted attachments, and establishing incident response procedures for handling potential service disruption events. The vulnerability underscores the critical importance of maintaining up-to-date security extensions and the necessity of thorough testing for edge cases in cryptographic software implementations.