CVE-2011-3481 in Cyrus IMAP Server
Summary
by MITRE
The index_get_ids function in index.c in imapd in Cyrus IMAP Server before 2.4.11, when server-side threading is enabled, allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via a crafted References header in an e-mail message.
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Analysis
by VulDB Data Team • 11/18/2021
The vulnerability described in CVE-2011-3481 represents a critical denial of service flaw within the Cyrus IMAP Server's email indexing mechanism. This issue affects versions prior to 2.4.11 and specifically targets the index_get_ids function located in the index.c file of the imapd component. The vulnerability becomes exploitable when server-side threading is enabled, creating a scenario where maliciously crafted email messages can trigger system instability. The flaw manifests through a NULL pointer dereference condition that ultimately leads to daemon crash, effectively rendering the email service unavailable to legitimate users.
The technical root cause of this vulnerability lies in insufficient input validation within the email header processing logic. When the imapd server processes email messages with crafted References headers, the index_get_ids function fails to properly handle edge cases in the header parsing routine. This failure results in a NULL pointer dereference during the server-side threading operation, which is a core functionality for organizing email conversations. The vulnerability demonstrates poor error handling practices and inadequate boundary checking in the email message processing pipeline, creating an exploitable condition that remote attackers can leverage without requiring authentication or privileged access. This type of flaw falls under CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by attackers to systematically degrade email service availability. Since the vulnerability affects the core IMAP daemon functionality, any successful exploitation results in immediate service termination requiring manual intervention to restore system operations. The attack vector is particularly concerning as it requires only the ability to send specially crafted email messages to the target server, making it accessible to anyone with basic email sending capabilities. This vulnerability directly impacts the availability aspect of the CIA triad and can be classified under ATT&CK technique T1499.100 which focuses on network denial of service attacks through service interruption.
Organizations affected by this vulnerability should prioritize immediate patching of their Cyrus IMAP Server installations to version 2.4.11 or later, which contains the necessary fixes for the NULL pointer dereference issue. Additionally, administrators should implement proper email filtering mechanisms to detect and block suspicious References headers, though this approach provides only partial protection as the vulnerability can be exploited through various header combinations. Network monitoring should be enhanced to detect unusual daemon crash patterns that may indicate exploitation attempts. The fix implemented in version 2.4.11 addresses the core issue by adding proper input validation and null pointer checks within the index_get_ids function, ensuring that malformed References headers do not cause the daemon to crash. Security teams should also consider implementing rate limiting on email processing and regular security assessments of email server configurations to prevent similar vulnerabilities from emerging in other components of the email infrastructure.