CVE-2026-21720 is a denial-of-service vulnerability affecting Grafana Enterprise version 3.0.0. The root cause lies in the handling of /avatar/:hash HTTP requests that are uncached. Each such request spawns a goroutine responsible for refreshing the Gravatar image. These goroutines are queued in a 10-slot worker queue. If the queue delay exceeds three seconds, the HTTP handler times out and stops listening for the goroutine's result. However, the goroutine itself remains blocked indefinitely because it attempts to send data on an unbuffered channel that no longer has a receiver. This results in goroutine leakage, where the number of blocked goroutines grows linearly with sustained traffic containing random avatar hashes. Over time, this leads to memory exhaustion and crashes of the Grafana server, causing denial of service. The vulnerability can be triggered remotely without authentication or user interaction, making it accessible to unauthenticated attackers. The CVSS v3.1 score of 7.5 reflects the high impact on availability with no impact on confidentiality or integrity. No patches or exploits are currently reported, but the vulnerability is publicly disclosed and should be addressed promptly.

For European organizations, the primary impact is denial of service due to Grafana server crashes caused by memory exhaustion. Grafana is widely used for monitoring and observability in enterprise IT environments, including critical infrastructure, financial services, and telecommunications. An outage of Grafana can disrupt monitoring capabilities, delaying detection of other security incidents or operational issues. This can increase the risk of prolonged downtime or cascading failures in IT systems. Organizations relying on Grafana Enterprise 3.0.0 are particularly vulnerable, as the issue can be exploited remotely without authentication. The impact is more severe for entities with high traffic volumes or public-facing Grafana instances, as attackers can easily generate the necessary traffic to trigger the vulnerability. The lack of known exploits in the wild currently reduces immediate risk, but the public disclosure means attackers could develop exploits rapidly. European sectors with stringent uptime requirements, such as energy, healthcare, and finance, face increased operational and reputational risks.

Immediate mitigation involves upgrading Grafana Enterprise to a version where this vulnerability is fixed; organizations should monitor Grafana’s official channels for patches. In the absence of a patch, administrators can implement rate limiting on the /avatar/:hash endpoint to restrict the number of uncached avatar requests and prevent excessive goroutine spawning. Deploying Web Application Firewalls (WAFs) or reverse proxies to filter or block suspicious traffic patterns targeting avatar hashes can reduce attack surface. Monitoring goroutine counts and memory usage on Grafana servers can provide early warning signs of exploitation attempts. Network segmentation to isolate Grafana instances and restricting access to trusted IP ranges can limit exposure. Additionally, disabling Gravatar image refresh functionality if not essential can eliminate the attack vector. Regular backups and incident response plans should be updated to handle potential Grafana outages. Finally, organizations should conduct penetration testing to verify the effectiveness of mitigations.