CVE-2006-5973 in Dovecot
Summary
by MITRE
Off-by-one buffer overflow in Dovecot 1.0test53 through 1.0.rc14, and possibly other versions, when index files are used and mmap_disable is set to "yes," allows remote authenticated IMAP or POP3 users to cause a denial of service (crash) via unspecified vectors involving the cache file.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 04/27/2026
The vulnerability described in CVE-2006-5973 represents a critical buffer overflow condition affecting Dovecot email servers running specific versions from 1.0test53 through 1.0.rc14, with potential impacts extending to other releases in the same lineage. This flaw manifests specifically when the mail server operates with index files and has the mmap_disable configuration parameter set to "yes," creating a dangerous combination that exposes the system to remote exploitation by authenticated users. The vulnerability operates through an off-by-one error in memory management, where the buffer boundary is incorrectly calculated, leading to memory corruption that can result in application crashes and denial of service conditions.
The technical implementation of this vulnerability involves the interaction between Dovecot's caching mechanism and memory mapping behaviors when the mmap_disable setting is active. When users access index files through IMAP or POP3 protocols, the application processes these requests in a manner that fails to properly validate buffer boundaries during cache operations. The off-by-one error occurs during the handling of cache file operations, where the application calculates buffer sizes or memory offsets incorrectly by precisely one byte, allowing malicious input to overwrite adjacent memory locations. This type of vulnerability falls under CWE-121, which specifically addresses stack-based buffer overflow conditions, though the exact manifestation involves memory management rather than stack corruption. The vulnerability is particularly concerning because it requires only authenticated access to exploit, meaning that legitimate users with valid credentials can trigger the denial of service condition without requiring special privileges or network-level access.
The operational impact of CVE-2006-5973 extends beyond simple service disruption to potentially compromise the integrity of email services within organizations relying on Dovecot implementations. When exploited, the vulnerability results in immediate application crashes that force the mail server to restart or become unresponsive, effectively denying legitimate users access to their email accounts and potentially causing data loss or message queue corruption. The remote nature of the attack means that malicious actors can exploit this vulnerability from anywhere on the network, provided they have valid user credentials, making it particularly dangerous in environments where email services are critical for business operations. Organizations using affected Dovecot versions face significant risk of service interruptions that could impact productivity and potentially expose sensitive email communications to unauthorized access during system recovery periods.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected Dovecot installations to versions that address the buffer overflow condition and implement proper memory boundary validation. System administrators should disable the mmap_disable setting when index files are in use, as this configuration parameter directly contributes to the vulnerability's exploitation. Additionally, implementing network segmentation and access controls can help limit the potential impact by restricting which users can access email services and by monitoring for unusual login patterns that might indicate exploitation attempts. The vulnerability's classification under ATT&CK technique T1499.004, which covers network denial of service, highlights the importance of implementing proper input validation and memory management practices in email server implementations. Organizations should also consider deploying intrusion detection systems to monitor for patterns consistent with buffer overflow exploitation attempts and establish robust backup and recovery procedures to minimize service disruption during remediation efforts.