CVE-2016-5826 in libical
Summary
by MITRE
The parser_get_next_char function in libical 0.47 and 1.0 allows remote attackers to cause a denial of service (out-of-bounds heap read) by crafting a string to the icalparser_parse_string function.
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Analysis
by VulDB Data Team • 05/15/2026
The vulnerability identified as CVE-2016-5826 represents a critical heap-based buffer overflow condition within the libical library version 0.47 and 1.0. This issue resides in the parser_get_next_char function which processes input strings through the icalparser_parse_string function, creating a pathway for remote attackers to execute denial of service attacks. The flaw occurs when maliciously crafted input strings are processed by the calendar parsing functionality, specifically targeting the memory management operations within the library's parsing engine. The vulnerability demonstrates a classic out-of-bounds heap read condition where the parser attempts to access memory locations beyond the allocated heap buffer boundaries, potentially leading to application crashes or system instability.
The technical implementation of this vulnerability stems from inadequate input validation and boundary checking within the parser's character processing logic. When the icalparser_parse_string function receives malformed input data, the parser_get_next_char function fails to properly validate array indices or buffer limits before attempting memory access operations. This deficiency creates an exploitable condition where an attacker can craft specific string sequences that cause the parser to read beyond allocated memory segments, resulting in unpredictable behavior and system resource exhaustion. The vulnerability manifests as a heap read operation that extends beyond the intended buffer limits, potentially causing memory corruption or application termination.
From an operational perspective, this vulnerability poses significant risks to systems that rely on libical for calendar and scheduling functionality, particularly in enterprise environments where calendar servers and collaborative platforms are prevalent. The remote exploitation capability means that attackers can trigger the denial of service condition without requiring local access or authentication, making it particularly dangerous for web-based calendar services, email servers, and unified communications platforms. The impact extends beyond simple service disruption to potentially affect business continuity, as calendar systems often serve as critical infrastructure components for scheduling, resource allocation, and workflow management. Organizations utilizing libical in production environments face potential downtime and reduced system availability when this vulnerability is exploited.
The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions in software systems, and represents a common pattern of memory safety issues that have been extensively documented in security research. From an attack framework perspective, this vulnerability could be categorized under ATT&CK technique T1499.004, which involves network denial of service attacks targeting applications and services. The exploitation of this vulnerability typically requires minimal technical expertise and can be automated through fuzzing tools or scripted attack vectors. Mitigation strategies should focus on immediate patching of affected libical versions, input validation enhancements, and implementation of proper bounds checking mechanisms within the parsing routines. Additionally, network segmentation and application-level firewalls can provide additional defense-in-depth measures to limit potential exploitation vectors and reduce the attack surface for this specific vulnerability.