# CVE-2021-37698: Missing TLS service certificate validation in GelfWriter, ElasticsearchWriter, InfluxdbWriter and Influxdb2Writer

> Attackers can intercept TLS traffic to time-series databases due to missing certificate validation in Icinga 2 writers, exposing sensitive monitoring data.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Aug 2021
- **Updated:** 3 Nov 2025
- **Also known as:** DEBIAN-CVE-2021-37698, GHSA-cxfm-8j5v-5qr2, UBUNTU-CVE-2021-37698

## What is CVE-2021-37698?

CVE-2021-37698 is a high-severity vulnerability in Debian Debian Linux, published on 19 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Icinga is a monitoring system which checks the availability of network resources, notifies users of outages, and generates performance data for reporting. In versions 2.5.0 through 2.13.0, ElasticsearchWriter, GelfWriter, InfluxdbWriter and Influxdb2Writer do not verify the server's certificate despite a certificate authority being specified. Icinga 2 instances which connect to any of the mentioned time series databases (TSDBs) using TLS over a spoofable infrastructure should immediately upgrade to version 2.13.1, 2.12.6, or 2.11.11 to patch the issue. Such instances should also change the credentials (if any) used by the TSDB writer feature to authenticate against the TSDB. There are no workarounds aside from upgrading.

Weakness: CWE-295 (Improper Certificate Validation)

## Which versions are affected by CVE-2021-37698?

It affects 2 products.


Products: Debian Debian Linux, Icinga Icinga.

## How do I fix CVE-2021-37698?

Upgrade to a fixed version.

## Is CVE-2021-37698 being exploited?

There is no known exploitation of CVE-2021-37698 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
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- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-37698 and fix it if it is affected.

What it is: CVE-2021-37698 is a high-severity vulnerability in Debian Debian Linux, published on 19 Aug 2021. 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-2021-37698 in the wild and no public exploit code.

Affected product: Debian Debian Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2021-37698/ (Markdown: https://insights.sbomify.com/CVE-2021-37698/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-37698
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-37698
- OSV: https://osv.dev/vulnerability/CVE-2021-37698

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-37698/
Summaries are generated and may contain mistakes; the official description above is the record.