CVE-2016-5827 in libical
Summary
by MITRE
The icaltime_from_string function in libical 0.47 and 1.0 allows remote attackers to cause a denial of service (out-of-bounds heap read) via a crafted string to the icalparser_parse_string function.
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Analysis
by VulDB Data Team • 05/15/2026
The vulnerability identified as CVE-2016-5827 represents a critical heap-based out-of-bounds read flaw within the libical library version 0.47 and 1.0. This issue specifically affects the icaltime_from_string function which processes calendar time data through the icalparser_parse_string function. The flaw manifests when maliciously crafted strings are processed by the calendar parsing functionality, potentially leading to system instability and denial of service conditions. The vulnerability resides in the library's inability to properly validate input data before attempting to parse calendar time components, creating an exploitable condition where attacker-controlled data can trigger memory access violations.
The technical implementation of this vulnerability stems from inadequate bounds checking within the time parsing logic. When the icaltime_from_string function receives malformed input through icalparser_parse_string, it attempts to read memory locations beyond the allocated heap buffer boundaries. This occurs because the parsing routine does not sufficiently validate the length or structure of incoming calendar time strings before performing array indexing operations. The flaw is classified as a heap-based buffer overflow condition that operates at the heap memory level rather than stack memory, making it particularly challenging to detect and exploit. This type of vulnerability typically maps to CWE-125: Out-of-bounds Read, which is categorized under the broader class of memory safety issues that affect software applications processing structured data.
The operational impact of CVE-2016-5827 extends beyond simple denial of service conditions to potentially compromise system availability and stability. When exploited, the vulnerability can cause applications using libical to crash or become unresponsive, effectively denying service to legitimate users. This is particularly concerning in calendar and scheduling applications where libical is commonly used for processing iCalendar data, including email clients, calendar servers, and collaboration platforms. The vulnerability affects systems that process external calendar data from untrusted sources, making it exploitable in scenarios where users might receive calendar invitations or import calendar files from unknown origins. Attackers can leverage this flaw to create persistent denial of service conditions against calendar services, potentially impacting enterprise environments where calendar synchronization is critical for business operations.
Mitigation strategies for CVE-2016-5827 should focus on immediate patching of affected libical versions, as version 1.0.1 and later contain fixes for this vulnerability. Organizations should prioritize updating their calendar applications and systems that depend on libical to prevent exploitation. Additionally, input validation should be implemented at the application level to sanitize calendar data before processing, though this approach is less reliable than patching the underlying library. Network segmentation and access controls can help limit exposure by restricting access to calendar services that process external data. Monitoring for unusual application crashes or memory access patterns can provide early detection of exploitation attempts. The vulnerability's impact aligns with ATT&CK technique T1499.004: Endpoint Denial of Service, which involves techniques that target system resources to prevent legitimate use. Security teams should also consider implementing application whitelisting and runtime protection mechanisms to prevent exploitation of this type of memory corruption vulnerability in environments where patching may be delayed.