CVE-2026-21720
Published: 27 January 2026
Summary
CVE-2026-21720 is a high-severity Uncontrolled Resource Consumption (CWE-400) vulnerability in Grafana Grafana. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 11.1th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SC-6 (Resource Availability).
Deeper analysis
CVE-2026-21720 is a denial-of-service vulnerability in Grafana affecting the /avatar/:hash endpoint. Every uncached request to this endpoint spawns a goroutine to refresh the corresponding Gravatar image. When the refresh operation queues up in the 10-slot worker queue and exceeds the three-second handler timeout, the handler stops listening for the result, leaving the goroutine blocked indefinitely while attempting to send on an unbuffered channel. Under sustained traffic with random hashes, this repeatedly triggers timeouts, causing goroutine counts to grow linearly, exhausting memory and crashing Grafana instances on some systems. The issue maps to CWE-400 (Uncontrolled Resource Consumption) and CWE-703 (Improper Check or Handling of Exceptional Conditions), with a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
Any unauthenticated attacker with network access to a vulnerable Grafana instance can exploit this by sending a high volume of requests to /avatar/:hash with random or uncached hashes. This low-complexity attack requires no privileges or user interaction and leads to resource exhaustion, rendering the service unavailable through memory depletion and process crashes.
The official Grafana security advisory provides details on patches and mitigation steps at https://grafana.com/security/security-advisories/CVE-2026-21720.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-4841
Vulnerability details
Every uncached /avatar/:hash request spawns a goroutine that refreshes the Gravatar image. If the refresh sits in the 10-slot worker queue longer than three seconds, the handler times out and stops listening for the result, so that goroutine blocks forever…
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trying to send on an unbuffered channel. Sustained traffic with random hashes keeps tripping this timeout, so goroutine count grows linearly, eventually exhausting memory and causing Grafana to crash on some systems.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Direct exploitation of public-facing Grafana app via crafted requests to trigger unbounded goroutine/resource exhaustion and crash (CWE-400).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
SC-5 enforces denial-of-service protections at entry points like the /avatar/:hash endpoint to block high-volume requests that trigger goroutine exhaustion.
SC-6 allocates and limits system resources such as memory and processes per user or request to prevent linear goroutine growth leading to exhaustion.
SI-2 requires timely flaw remediation including patching the specific vulnerability causing blocked goroutines on timeout in Grafana.