Denial of service via recursive equality comparisons
Published Aug 25, 2026 · Updated Aug 25, 2026
Algorithmic complexity in icalendar 7.1.0 through 7.1.2 allows remote attackers to cause a CPU hang via crafted .ics data. Component.eq uses two membership loops whose child comparisons recursively repeat at every nesting level, producing exponential work on equal nested subtrees. Exploitation requires a consuming application to compare attacker-supplied components; parsing alone does not trigger the service interruption.
Summary
What happened
Algorithmic complexity in icalendar 7.1.0 through 7.1.2 allows remote attackers to cause a CPU hang via crafted .ics data. Component.eq uses two membership loops whose child comparisons recursively repeat at every nesting level, producing exponential work on equal nested subtrees. Exploitation requires a consuming application to compare attacker-supplied components; parsing alone does not trigger the service interruption.
The record
- CVE
- CVE-2026-55099
- Published
- Aug 25, 2026
- Updated
- Aug 25, 2026
- Vendor
- Collective
- Product
- icalendar
- Classifications
- CWE-407, CWE-400, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 25, 2026CVE publishedPublication date reported by the CVE source.
- Aug 25, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 7.1.0, < 7.1.3
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Upstream nested-component comparison proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo