CVE-2001-1154 in Cyrus IMAP Server
Summary
by MITRE
Cyrus 2.0.15, 2.0.16, and 1.6.24 on BSDi 4.2, with IMAP enabled, allows remote attackers to cause a denial of service (hang) using PHP IMAP clients.
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Analysis
by VulDB Data Team • 04/08/2019
The vulnerability described in CVE-2001-1154 represents a significant denial of service weakness within the Cyrus IMAP server software versions 2.0.15, 2.0.16, and 1.6.24 running on BSDi 4.2 systems. This issue specifically targets the IMAP protocol implementation and demonstrates how seemingly innocuous client interactions can be exploited to disrupt service availability. The vulnerability arises from the server's inadequate handling of certain PHP IMAP client requests, creating a condition where legitimate service operations can be interrupted through carefully crafted remote inputs. The affected environment includes BSDi 4.2 operating systems which were prevalent during the early 2000s era, making this a historical yet instructive example of protocol-level security flaws that could impact email server availability.
The technical flaw manifests when PHP IMAP clients establish connections to the Cyrus IMAP server and perform specific operations that trigger an infinite loop or resource exhaustion condition within the server's processing logic. This occurs because the server fails to properly validate or limit the processing of certain IMAP command sequences that PHP clients generate, particularly those involving mailbox operations or message retrieval commands. The vulnerability leverages the interaction between the PHP IMAP extension and the Cyrus server implementation, where the server's response handling mechanism becomes trapped in a state where it cannot properly process subsequent requests or maintain normal service operations. This behavior aligns with CWE-400, which categorizes unchecked resource consumption as a fundamental weakness in software design that can lead to denial of service conditions.
The operational impact of this vulnerability extends beyond simple service interruption to potentially compromise the overall reliability and availability of email services within organizations relying on Cyrus IMAP servers. When exploited successfully, the vulnerability causes the IMAP server to hang or become unresponsive, effectively preventing legitimate users from accessing their email accounts through IMAP clients. This disruption can cascade into broader system issues, particularly in environments where email services are critical for business operations or communication workflows. The remote nature of the attack means that adversaries can exploit this weakness from outside the network perimeter without requiring authentication or privileged access, making it particularly dangerous for publicly accessible email servers. Organizations using affected versions of Cyrus IMAP were vulnerable to this type of attack that could be executed with minimal technical expertise and resources.
Mitigation strategies for this vulnerability primarily involve immediate software updates to patched versions of the Cyrus IMAP server that address the specific handling of PHP IMAP client requests. System administrators should prioritize upgrading to versions that contain fixes for the resource consumption and input validation issues that enable this denial of service condition. Additionally, implementing network-level controls such as rate limiting and connection monitoring can help detect and prevent exploitation attempts. The vulnerability also underscores the importance of proper protocol implementation and input validation, which aligns with ATT&CK technique T1499.004 for network denial of service attacks. Organizations should also consider deploying intrusion detection systems that can identify unusual patterns of IMAP traffic that might indicate exploitation attempts. Regular security assessments and vulnerability scanning of email infrastructure remain essential practices to identify and remediate similar weaknesses before they can be exploited by malicious actors.