CVE-2016-9584 in libical
Summary
by MITRE
libical allows remote attackers to cause a denial of service (use-after-free) and possibly read heap memory via a crafted ics file.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2016-9584 affects the libical library, a widely used open-source implementation of the iCalendar standard for handling calendar data. This library is integral to numerous applications including email clients, calendar applications, and collaboration platforms that process iCalendar files. The flaw manifests as a use-after-free condition that occurs when the library processes malformed iCalendar (.ics) files, creating a critical security risk for systems that rely on this component for calendar data processing.
The technical implementation of this vulnerability involves a specific flaw in how libical handles memory allocation and deallocation during the parsing of iCalendar data structures. When a maliciously crafted .ics file is processed, the library's parser fails to properly validate the structure of the input data, leading to a situation where memory that has been freed is subsequently accessed. This use-after-free condition creates a predictable pattern of memory corruption that can be exploited by remote attackers to cause system instability or potentially execute arbitrary code. The vulnerability specifically targets the heap memory management within the library's parsing routines, where the attacker can manipulate the calendar data to trigger the memory corruption.
The operational impact of this vulnerability extends beyond simple denial of service, as the use-after-free condition can potentially be leveraged for more sophisticated attacks. Remote attackers can craft malicious .ics files that, when processed by vulnerable applications, will cause the target system to crash or behave unpredictably. The heap memory read operations that may occur as a result of this flaw could potentially expose sensitive data from the application's memory space, though the primary risk remains the denial of service and potential code execution. This vulnerability affects any system that uses libical for processing calendar data, including enterprise email systems, collaboration platforms, and mobile calendar applications.
Mitigation strategies for CVE-2016-9584 should prioritize immediate patching of affected libical versions, as the vulnerability is well-documented and remediation is available through updated library releases. Organizations should implement strict input validation for all calendar data processing, particularly for files received from external sources. Network segmentation and access controls can help limit the potential impact of exploitation attempts, while monitoring systems should be configured to detect unusual memory access patterns or application crashes. The vulnerability aligns with CWE-416, which addresses use-after-free conditions, and represents a classic example of how improper memory management can create security risks that align with techniques described in the ATT&CK framework under defense evasion and execution tactics. Regular security assessments and dependency updates are essential to prevent exploitation of similar memory corruption vulnerabilities in other components of the system stack.