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

> Unauthenticated attackers can cause Grafana to crash by exhausting memory through goroutine leaks triggered by timed-out avatar requests.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Jan 2026
- **Updated:** 27 Aug 2026
- **Also known as:** BIT-grafana-2026-21720, CLSA-2026-1775824794, CLSA-2026-1775825437, GHSA-m4rj-q4ph-fr4v, MINI-2chx-2fp4-x7hx, MINI-3fwr-w8hj-3c9m, MINI-7hcq-3q76-94g5, MINI-8gqf-6545-p7cp, MINI-f8p3-vcvj-4544, MINI-fmjp-w24w-228r, MINI-gfh8-pw32-mpjc, MINI-gx42-9h47-2q8q, MINI-h268-xc7j-f3gp, MINI-h9hx-g4fr-mhm4, MINI-j45x-76m7-cv2m, MINI-jh9q-52v6-prvq, MINI-p7f5-jcmx-58x3, MINI-w453-mrwc-45pv, UBUNTU-CVE-2026-21720

## What is CVE-2026-21720?

CVE-2026-21720 is a high-severity denial of service vulnerability in Grafana Grafana, published on 27 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-772 (Missing Release of Resource after Effective Lifetime), CWE-703 (Improper Check or Handling of Exceptional Conditions), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-21720?

1 open source package ship an affected version, including grafana. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `grafana` | Bitnami | From 3.0.0 | 11.6.9, 12.0.8, 12.1.5, 12.2.3, 12.3.1 |

Products: Grafana Grafana.

## How do I fix CVE-2026-21720?

Upgrade grafana to a fixed version for your release line: 11.6.9, 12.0.8, 12.1.5 or 12.2.3.

## Is CVE-2026-21720 being exploited?

There is no known exploitation of CVE-2026-21720 in the wild and no public exploit code.

## Other vulnerabilities in Grafana Grafana

- [CVE-2021-43798](https://insights.sbomify.com/CVE-2021-43798/): Grafana Path Traversal (high 7.5, exploited in the wild)
- [CVE-2025-41115](https://insights.sbomify.com/CVE-2025-41115/): Incorrect privilege assignment (critical 10.0)
- [CVE-2022-39328](https://insights.sbomify.com/CVE-2022-39328/): Grafana vulnerable to race condition allowing privilege escalation (critical 9.8)
- [CVE-2022-28660](https://insights.sbomify.com/CVE-2022-28660/): Auth bypass in n/a (critical 9.8)
- [CVE-2022-26148](https://insights.sbomify.com/CVE-2022-26148/): Information disclosure in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-21720 and fix it if it is affected.

What it is: CVE-2026-21720 is a high-severity denial of service vulnerability in Grafana Grafana, published on 27 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-21720 in the wild and no public exploit code.

Affected packages and fixed versions:
- grafana (Bitnami): affected from 3.0.0; fixed in 11.6.9, 12.0.8, 12.1.5, 12.2.3, 12.3.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-21720/ (Markdown: https://insights.sbomify.com/CVE-2026-21720/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21720
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21720
- OSV: https://osv.dev/vulnerability/CVE-2026-21720

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21720/
Summaries are generated and may contain mistakes; the official description above is the record.