CVE-2026-55099 collective CVE debrief

Who should care

Defenders responsible for calendar sync or import endpoints, invite processing, and other comparison paths should assess exposure and prioritize patching or mitigation. This includes operators, platform administrators, vulnerability management teams, and security teams who need to review and implement necessary controls to prevent denial-of-service attacks.

Why it matters

Defenders should prioritize patching or mitigating CVE-2026-55099 due to potential denial-of-service impacts in calendar-related applications.

• Denial of service in calendar sync or import endpoints
• CPU usage increase potentially leading to performance degradation
• Potential for service interruption or slowdown

Technical summary

The icalendar library's Component equality method has a vulnerability that causes O(2^n) work relative to nesting depth when comparing nested subcomponents. This can lead to excessive CPU usage and denial of service when an attacker crafts a malicious .ics file. The vulnerability is caused by the Component equality method in src/icalendar/cal/component.py, which compares nested subcomponents with two membership loops, leading to O(2^n) work relative to nesting depth. Parsing alone does not trigger the issue, but comparisons that differ early short-circuit can be affected.

Defensive priority

Defenders should prioritize patching or mitigating this vulnerability, especially in calendar sync or import endpoints, invite processing, and other comparison paths.

Recommended defensive actions

• Patch to version 7.1.3 or later
• Validate and sanitize .ics file inputs
• Implement rate limiting on calendar sync or import endpoints
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The vulnerability is caused by the Component equality method in src/icalendar/cal/component.py, which compares nested subcomponents with two membership loops, leading to O(2^n) work relative to nesting depth.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.