CVE-2026-21720 | Unauthenticated DoS: avatar cache leaks goroutines when /avatar/:hash requests time out

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 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.

Published: 2026-01-27 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-21720 is rated Moderate Risk (43.4/100): CVSS High severity, with low exploitation likelihood (EPSS 0.47%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-21720

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.02% 0.47% +0.46%
2 2026-02-18 0.05% 0.02% -0.03%
3 2026-02-02 — 0.05% —

Full EPSS history (4 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-21720

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2026-21720

OS Trackers for CVE-2026-21720

vendor priority summary link
alpine — CVE-2026-21720: 1 source package rows (grafana); 43 state rows across 2 repos (3.23-community, edge-community); fixed 0, open 43. https://security.alpinelinux.org/vuln/CVE-2026-21720
redhat high — https://access.redhat.com/security/cve/CVE-2026-21720
suse high CVE-2026-21720 severity important: SUSE including 26 source package names (dracut-saltboot-1.1.0-150000.1.65.1, firewalld-prometheus-config-0.1-150000.3.67.1, …), 52 product×package rows across 9 product lines (Container suse/manager/5.0/x86_64/server, SUSE Linux Enterprise Module for Package Hub 15 SP7, … (9 product lines)): Fixed 37, First Fixed 15. https://www.suse.com/security/cve/CVE-2026-21720/
ubuntu medium CVE-2026-21720 medium priority: Ubuntu including 1 source packages (grafana), 5 status rows across 5 suites (jammy, noble, questing, upstream, xenial): DNE 3, needs-triage 2. https://ubuntu.com/security/CVE-2026-21720

Affected software / configurations for CVE-2026-21720

Vendor Product Version Raw CPE
grafana grafana >= 3.0.0, < 11.6.9 cpe:2.3:a:grafana:grafana:*:*:*:*:-:*:*:*
grafana grafana >= 3.0.0, < 11.6.9 cpe:2.3:a:grafana:grafana:*:*:*:*:enterprise:*:*:*
grafana grafana >= 12.0.0, < 12.0.8 cpe:2.3:a:grafana:grafana:*:*:*:*:-:*:*:*
grafana grafana >= 12.0.0, < 12.0.8 cpe:2.3:a:grafana:grafana:*:*:*:*:enterprise:*:*:*
grafana grafana >= 12.1.0, < 12.1.5 cpe:2.3:a:grafana:grafana:*:*:*:*:-:*:*:*
grafana grafana >= 12.1.0, < 12.1.5 cpe:2.3:a:grafana:grafana:*:*:*:*:enterprise:*:*:*
grafana grafana >= 12.2.0, < 12.2.3 cpe:2.3:a:grafana:grafana:*:*:*:*:-:*:*:*
grafana grafana >= 12.2.0, < 12.2.3 cpe:2.3:a:grafana:grafana:*:*:*:*:enterprise:*:*:*
grafana grafana 12.3.0 cpe:2.3:a:grafana:grafana:12.3.0:*:*:*:-:*:*:*
grafana grafana 12.3.0 cpe:2.3:a:grafana:grafana:12.3.0:*:*:*:enterprise:*:*:*

References for CVE-2026-21720

cvelogic Threat Intelligence