Inviting excessive long email addresses to a calendar event makes the Nextcloud server unresponsive

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

• nextcloud calendar1.0 and later · before 4.4.4

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

• nextcloud security-advisories

  • >= 1.0.0, < 4.4.4affected

Other highest-scoring records for the same primary product.

• CVE-2022-24838Command Injection in Appointment Emails for Nextcloud Calendar
  49Plan
• CVE-2025-66511Nextcloud Calendar app used predictable proposal participant tokens
  26Monitor
• CVE-2023-48308Calendar app returns full stacktrace when an error happens while editing appointment
  26Monitor
• CVE-2025-66550Nextcloud Calendar attachments of local files are offered to downloaded
  22Monitor
• CVE-2018-3763In Nextcloud Calendar before 1.5.8 and 1.6.1, a missing sanitization of search results for an autocomplete field could lead to a stored XSS
  19Monitor
• CVE-2024-37316Nextcloud Calendar's event create can create attachments that link to other websites
  18Monitor

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

1function expand(node) {2  return node.children.map(expand);3}

1const MAX_DEPTH = 32;2function expand(node, depth = 0) {3  if (depth > MAX_DEPTH) throw new Error("too deep");4  return node.children.map((c) => expand(c, depth + 1));5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.