CVE-2019-11356 in Cyrus IMAP Server
Summary
by MITRE
The CalDAV feature in httpd in Cyrus IMAP 2.5.x through 2.5.12 and 3.0.x through 3.0.9 allows remote attackers to execute arbitrary code via a crafted HTTP PUT operation for an event with a long iCalendar property name.
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Analysis
by VulDB Data Team • 09/26/2023
The vulnerability CVE-2019-11356 represents a critical remote code execution flaw in the Cyrus IMAP server's CalDAV implementation that affects versions 2.5.x through 2.5.12 and 3.0.x through 3.0.9. This vulnerability specifically targets the HTTP PUT operation handling within the CalDAV subsystem, which is used for managing calendar events and scheduling information. The flaw arises from insufficient input validation and buffer handling when processing iCalendar property names, creating a path for attackers to inject malicious payloads through crafted calendar data. The vulnerability is categorized under CWE-121 as a stack-based buffer overflow, which occurs when the server fails to properly validate the length of iCalendar property names during HTTP PUT operations.
The technical exploitation of this vulnerability involves crafting a malicious iCalendar event with an excessively long property name that exceeds the buffer size allocated by the Cyrus IMAP server. When the server processes this malformed calendar data during the HTTP PUT operation, it writes beyond the allocated memory space, potentially overwriting adjacent memory locations including return addresses and function pointers. This memory corruption can be leveraged by attackers to execute arbitrary code with the privileges of the Cyrus IMAP service account, which typically runs with elevated system permissions. The attack vector is particularly dangerous because it requires no authentication for the initial exploitation, making it a significant threat to systems where CalDAV is enabled and accessible over the network.
From an operational impact perspective, successful exploitation of CVE-2019-11356 can result in complete compromise of the affected Cyrus IMAP server. Attackers can gain remote code execution capabilities that allow them to establish persistent access, escalate privileges, and potentially move laterally within the network infrastructure. The vulnerability affects organizations that rely on Cyrus IMAP for email and calendar services, particularly those with public CalDAV endpoints or those that expose calendar services to untrusted networks. The attack surface is broad since many organizations use Cyrus IMAP for enterprise email solutions and calendar management, making this vulnerability particularly concerning for large organizations with extensive calendar infrastructure. Security professionals should note that this vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as successful exploitation would likely involve executing shell commands through the compromised service.
The recommended mitigation strategies for CVE-2019-11356 include immediate patching of affected Cyrus IMAP server versions to the latest stable releases that contain the fix for the buffer overflow vulnerability. Organizations should also implement network segmentation to restrict access to CalDAV endpoints, particularly for systems that do not require public calendar access. Additional protective measures include enabling proper input validation on all calendar data, implementing rate limiting for HTTP PUT operations, and monitoring for unusual calendar data patterns that might indicate exploitation attempts. Security teams should also consider disabling CalDAV functionality if it is not essential for business operations, as this provides the most effective defense against this specific vulnerability. The fix implemented by Cyrus IMAP developers involved proper bounds checking and input validation for iCalendar property names, preventing the buffer overflow condition that enabled arbitrary code execution. Organizations should also conduct thorough security assessments of their calendar infrastructure and review access controls to ensure that only authorized users can perform HTTP PUT operations that could trigger this vulnerability.