CVE-2026-111269 in libical
Summary
by MITRE • 10/16/2026
libical through 4.0.6 contains a heap-based out-of-bounds read in icalvalue_decode_ical_string() in src/libical/icalvalue.c when decoding input ending in a backslash. Attackers can supply escaped iCalendar text with a trailing backslash, causing the loop to read past the terminator and crash the application or leak adjacent heap memory.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability identified in libical versions through 4.0.6 represents a critical security flaw within the core parsing logic of the library, specifically located in the icalvalue_decode_ical_string function found in src/libical/icalvalue.c. This component is responsible for processing iCalendar data strings, which are widely used in scheduling and calendar applications to exchange meeting information, appointments, and other time-based events. The root cause of this vulnerability lies in how the library handles escaped characters within these text fields. When an input string contains escape sequences, particularly those ending with a backslash character, the decoding routine fails to correctly account for the bounds of the allocated memory buffer. This oversight leads directly to a heap-based out-of-bounds read condition, classified under CWE-125 in industry standard vulnerability taxonomies.
From a technical perspective, the flaw manifests when an attacker supplies iCalendar text that includes escaped characters followed by a trailing backslash at the end of the string. The decoding loop iterates through the input to resolve escape sequences but does not properly validate whether it has reached the null terminator or the actual end of the valid data range before attempting to read the next byte. Consequently, the function reads memory locations adjacent to the intended buffer boundary on the heap. This behavior violates fundamental principles of safe memory access and allows for unauthorized information disclosure or application instability depending on the state of the surrounding heap memory at runtime.
The operational impact of this vulnerability is significant for any software that relies on libical to parse untrusted iCalendar data, such as email clients, calendar servers, and scheduling applications. An attacker who can craft a maliciously formatted iCalendar file with a trailing backslash in an escaped text field can trigger the out-of-bounds read upon processing. This exploitation vector typically results in two primary outcomes: application crash or denial of service due to segmentation faults when accessing invalid memory addresses, and potential information leakage where sensitive data stored in adjacent heap regions is exposed through the malformed output. In complex environments involving automated parsing pipelines, this could also serve as a precursor for more sophisticated attacks if combined with other vulnerabilities that allow control over execution flow following the read operation.
Mitigation strategies must focus on both immediate patching and long-term defensive coding practices. The most effective remediation is to upgrade libical to version 4.0.7 or later, where this specific boundary check has been corrected in the source code. For organizations unable to immediately update their dependencies, implementing input validation at the application layer can provide a temporary defense-in-depth measure by rejecting iCalendar strings that contain trailing backslashes within escaped text fields before they are passed to the library's decoding functions. Furthermore developers should enforce strict adherence to RFC 5545 standards which define precise rules for escaping characters in iCalendar data, ensuring that parsers do not accept malformed inputs that deviate from expected syntax structures.
This vulnerability aligns with common attack patterns observed in real-world scenarios where attackers exploit parsing inconsistencies in widely used libraries to achieve remote code execution or service disruption. It is relevant to the MITRE ATT&CK framework under techniques involving resource injection and exploitation of software vulnerabilities for initial access or impact purposes. Security teams should prioritize reviewing their dependency trees for instances of libical below version 4.0.7 and apply patches promptly to mitigate risks associated with heap corruption and memory disclosure attacks targeting calendar-related services.