CVE-2026-55099

The record

icalendar is an RFC 5545 compatible parser and generator of iCalendar files for Python. From 7.1.0 until 7.1.3, the Component equality method in src/icalendar/cal/component.py compares nested subcomponents with two membership loops, and each membership test invokes the same method on child components, causing O(2^n) work relative to nesting depth. Component.from_ical accepts arbitrarily nested BEGIN:VEVENT blocks without a depth limit, so an attacker can submit a sub-kilobyte .ics file containing equal nested subtrees and trigger the cost when an application performs equality, inequality, membership, deduplication, test-assertion, round-trip, or normalization comparisons. Parsing alone does not trigger the issue, and comparisons that differ early short-circuit, but a few hundred bytes can pin a CPU core for minutes or indefinitely, causing denial of service in calendar sync or import endpoints, invite processing, and other comparison paths. This issue is fixed in version 7.1.3.

Affected packages

Related vulnerabilities

• CVE-2026-113795 pypdf is a free and open-source pure-python PDF library. CWE-400
• CVE-2026-83400 Vulnerability in the Oracle Java SE, Oracle GraalVM for JDK, Oracle GraalVM Enterprise… CWE-400
• CVE-2026-112400 Pillow is a Python imaging library. CWE-400
• CVE-2026-111766 markdown-it is a Markdown parser. CWE-400
• CVE-2026-111759 markdown-it is a Markdown parser. CWE-400
• CVE-2025-52290 A NULL pointer dereference in the avpriv_h264_has_num_reorder_frames function of Ffmpeg… CWE-400
• CVE-2026-111066 AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. CWE-400
• CVE-2026-59951 The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context… CWE-400