CVE-2016-5825 in libical
Summary
by MITRE
The icalparser_parse_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 ics file.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 05/15/2026
The vulnerability identified as CVE-2016-5825 affects the libical library version 0.47 and 1.0, specifically within the icalparser_parse_string function. This flaw represents a critical security issue that enables remote attackers to execute a denial of service attack through carefully crafted iCalendar (.ics) files. The vulnerability stems from improper input validation and memory handling within the parsing routine, creating an out-of-bounds heap read condition that can be exploited by malicious actors to disrupt system operations.
The technical implementation of this vulnerability involves the icalparser_parse_string function failing to properly validate the boundaries of heap memory when processing malformed iCalendar data. When a remote attacker submits a specially constructed .ics file, the parser attempts to read memory locations beyond the allocated heap buffer, resulting in an out-of-bounds heap read. This condition typically occurs during the parsing of calendar event data, particularly when encountering malformed or unexpected field values within the iCalendar format structure. The vulnerability is classified under CWE-125 as an out-of-bounds read, which represents a fundamental memory safety issue that can lead to system instability and denial of service conditions.
The operational impact of CVE-2016-5825 extends beyond simple service disruption to potentially compromise system availability and stability. When exploited, this vulnerability allows attackers to cause applications using libical to crash or become unresponsive, effectively creating a denial of service condition. Systems that rely on processing calendar data, such as email servers, calendar applications, and collaboration platforms, become vulnerable to this attack vector. The vulnerability is particularly concerning because it can be triggered remotely without requiring authentication, making it an attractive target for automated exploitation campaigns. The out-of-bounds memory access can lead to unpredictable behavior including application crashes, memory corruption, or even potential information disclosure depending on the system configuration and memory layout.
Mitigation strategies for CVE-2016-5825 should prioritize immediate software updates and patches from the libical maintainers. Organizations should upgrade to versions of libical that contain fixes for this vulnerability, typically those released after the vulnerability disclosure. Additionally, implementing input validation measures at the application level can provide defense-in-depth protection, where applications using libical can validate .ics file contents before processing them through the vulnerable parser. Network-level controls such as firewalls or intrusion detection systems can be configured to filter suspicious .ics file content or block traffic to affected services. The vulnerability aligns with ATT&CK technique T1499.004 for network denial of service and represents a classic example of how memory safety vulnerabilities in widely-used libraries can create widespread impact across multiple applications and systems. Administrators should also consider implementing monitoring and alerting for unusual application crashes or service disruptions that may indicate exploitation attempts.