CVE-2024-21658
📋 TL;DR
CVE-2024-21658 is a resource exhaustion vulnerability in the discourse-calendar plugin where overly generous region value length limits allow attackers to cause excessive bandwidth and disk space consumption. All Discourse instances using the vulnerable discourse-calendar plugin are affected. The vulnerability can degrade system performance and potentially lead to denial of service.
💻 Affected Systems
- discourse-calendar
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service through resource exhaustion, rendering the Discourse instance unavailable and potentially causing data loss or corruption.
Likely Case
Degraded performance, increased hosting costs due to bandwidth/disk usage, and temporary service disruptions.
If Mitigated
Minimal impact with proper monitoring and resource limits, though some performance degradation may still occur during attacks.
🎯 Exploit Status
Exploitation requires ability to create or modify calendar events with malicious region values.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Main branch (latest commit after fix)
Vendor Advisory: https://github.com/discourse/discourse-calendar/security/advisories/GHSA-65f2-9ghp-x8h8
Restart Required: Yes
Instructions:
1. Update discourse-calendar plugin to latest main branch
2. Restart Discourse instance
3. Verify the fix is applied
🧯 If You Can't Patch
- Disable the discourse-calendar plugin entirely
- Implement strict rate limiting and input validation at the application level
🔍 How to Verify
Check if Vulnerable:
Check if discourse-calendar plugin is installed and if version predates the main branch fixCheck Version:
Check Discourse admin panel or plugin directory for discourse-calendar versionVerify Fix Applied:
Verify plugin is updated to main branch commit after the fix and test calendar functionality📡 Detection & Monitoring
Log Indicators:
- Unusually large region values in calendar-related logs
- Spike in disk I/O or bandwidth usage
- Error logs related to resource limits
Network Indicators:
- Large HTTP requests to calendar endpoints
- Unusual traffic patterns to /calendar routes
SIEM Query:
source="discourse" AND ("calendar" OR "region") AND size>threshold