# CVE-2021-3422: Indexer denial-of-service via malformed S2S request

> Attackers can cause denial of service in Splunk Enterprise by sending malformed S2S requests to instances configured to index Universal Forwarder traffic.

- **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:** No
- **Published:** 25 Mar 2022
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-4c93-wvp2-c39r

## What is CVE-2021-3422?

CVE-2021-3422 is a high-severity denial of service vulnerability in Splunk Splunk, published on 25 Mar 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The lack of validation of a key-value field in the Splunk-to-Splunk protocol results in a denial-of-service in Splunk Enterprise instances configured to index Universal Forwarder traffic. The vulnerability impacts Splunk Enterprise versions before 7.3.9, 8.0 versions before 8.0.9, and 8.1 versions before 8.1.3. It does not impact Universal Forwarders. When Splunk forwarding is secured using TLS or a Token, the attack requires compromising the certificate or token, or both. Implementation of either or both reduces the severity to Medium.

Weakness: CWE-20 (Improper Input Validation), CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2021-3422?

It affects 1 product.


Products: Splunk Splunk.

## How do I fix CVE-2021-3422?

No fix has been published for CVE-2021-3422 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-3422 being exploited?

There is no known exploitation of CVE-2021-3422 in the wild and no public exploit code.

## Other vulnerabilities in Splunk Splunk

- [CVE-2026-20253](https://insights.sbomify.com/CVE-2026-20253/): Splunk Enterprise Missing Authentication for Critical Function (critical 9.8, exploited in the wild)
- [CVE-2026-76268](https://insights.sbomify.com/CVE-2026-76268/): Missing Authentication for Critical Function in the Patroni REST API in Splunk Enterprise (critical 9.8)
- [CVE-2026-76284](https://insights.sbomify.com/CVE-2026-76284/): Improper Neutralization in Splunk Enterprise (critical 9.8)
- [CVE-2026-76285](https://insights.sbomify.com/CVE-2026-76285/): Improper Adherence to Coding Standards in Splunk Enterprise (critical 9.8)
- [CVE-2017-17067](https://insights.sbomify.com/CVE-2017-17067/): Auth bypass in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3422 and fix it if it is affected.

What it is: CVE-2021-3422 is a high-severity denial of service vulnerability in Splunk Splunk, published on 25 Mar 2022. 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-2021-3422 in the wild and no public exploit code.

Affected product: Splunk Splunk. 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-2021-3422/ (Markdown: https://insights.sbomify.com/CVE-2021-3422/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3422
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3422
- OSV: https://osv.dev/vulnerability/CVE-2021-3422

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3422/
Summaries are generated and may contain mistakes; the official description above is the record.