CVE-2026-21720
📋 TL;DR
This vulnerability in Grafana allows attackers to cause denial of service by exhausting system memory through uncontrolled goroutine creation. Attackers can send sustained requests with random avatar hashes to trigger timeouts that create orphaned goroutines, eventually crashing the Grafana service. All Grafana instances with avatar caching enabled are affected.
💻 Affected Systems
- Grafana
📦 What is this software?
Grafana by Grafana
Grafana by Grafana
Grafana by Grafana
Grafana by Grafana
Grafana by Grafana
Grafana by Grafana
Grafana by Grafana
Grafana by Grafana
Grafana by Grafana
Grafana by Grafana
⚠️ Risk & Real-World Impact
Worst Case
Complete Grafana service outage with memory exhaustion leading to system instability or crash, potentially affecting monitoring and observability across an organization.
Likely Case
Service degradation and eventual crash of Grafana instances under sustained attack, disrupting monitoring dashboards and alerting capabilities.
If Mitigated
Minimal impact with proper rate limiting, network segmentation, and timely patching preventing successful exploitation.
🎯 Exploit Status
Exploitation requires sending HTTP requests to /avatar/:hash endpoints with random hashes; no authentication needed
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Grafana security advisory for specific patched versions
Vendor Advisory: https://grafana.com/security/security-advisories/CVE-2026-21720
Restart Required: Yes
Instructions:
1. Review Grafana security advisory for affected versions. 2. Upgrade to patched version. 3. Restart Grafana service. 4. Verify fix by checking version and monitoring goroutine count.
🔧 Temporary Workarounds
Disable Gravatar/Avatar Caching
allDisable avatar fetching functionality to prevent exploitation
Modify Grafana configuration to set [auth] disable_gravatar = true
Implement Rate Limiting
linuxAdd rate limiting at reverse proxy or application level to prevent sustained attack traffic
nginx: limit_req_zone $binary_remote_addr zone=avatar:10m rate=10r/s;
Add limit_req zone=avatar burst=20 nodelay; to location block
🧯 If You Can't Patch
- Implement strict network controls to limit access to Grafana avatar endpoints
- Deploy WAF rules to detect and block patterns of random hash requests to /avatar/ endpoints
🔍 How to Verify
Check if Vulnerable:
Check Grafana version against affected versions in security advisory; monitor goroutine count during avatar requestsCheck Version:
grafana-server -v or check web interface About pageVerify Fix Applied:
After patching, test with avatar requests and monitor that goroutine count stabilizes and doesn't grow unbounded📡 Detection & Monitoring
Log Indicators:
- High frequency of 404 or timeout errors on /avatar/ endpoints
- Increasing memory usage and goroutine count in Grafana logs
Network Indicators:
- Sustained HTTP requests to /avatar/ with random hash patterns
- Unusual traffic spikes to avatar endpoints
SIEM Query:
source="grafana" AND (uri_path="/avatar/*" OR message="goroutine" OR message="timeout") | stats count by src_ip