# CVE-2022-20653: Cisco Email Security Appliance DNS Verification Denial of Service Vulnerability

> Remote attackers can cause denial of service on Cisco Email Security Appliances by sending specially formatted emails that trigger insufficient error handling in DNS verification.

- **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:** 17 Feb 2022
- **Updated:** 6 Nov 2024
- **Also known as:** GHSA-p3pv-g3c9-4qf8

## What is CVE-2022-20653?

CVE-2022-20653 is a high-severity denial of service vulnerability in Cisco Asyncos, published on 17 Feb 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the DNS-based Authentication of Named Entities (DANE) email verification component of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient error handling in DNS name resolution by the affected software. An attacker could exploit this vulnerability by sending specially formatted email messages that are processed by an affected device. A successful exploit could allow the attacker to cause the device to become unreachable from management interfaces or to process additional email messages for a period of time until the device recovers, resulting in a DoS condition. Continued attacks could cause the device to become completely unavailable, resulting in a persistent DoS condition.

Weakness: CWE-399

## Which versions are affected by CVE-2022-20653?

It affects 1 product.


Products: Cisco Asyncos.

## How do I fix CVE-2022-20653?

No fix has been published for CVE-2022-20653 yet. Limit exposure of the affected software until one is available.

## Is CVE-2022-20653 being exploited?

There is no known exploitation of CVE-2022-20653 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Asyncos

- [CVE-2025-20393](https://insights.sbomify.com/CVE-2025-20393/): Cisco Multiple Products Improper Input Validation (critical 10.0, exploited in the wild)
- [CVE-2026-76519](https://insights.sbomify.com/CVE-2026-76519/): Cisco Secure Email Gateway Relative Path Traversal (critical 9.8, exploited in the wild)
- [CVE-2026-76461](https://insights.sbomify.com/CVE-2026-76461/): Cisco Secure Email Gateway SQL Injection (critical 9.8, exploited in the wild)
- [CVE-2024-20435](https://insights.sbomify.com/CVE-2024-20435/): Command injection in Cisco Secure Web Appliance (high 8.8)
- [CVE-2019-15956](https://insights.sbomify.com/CVE-2019-15956/): Cisco Web Security Appliance Unauthorized Device Reset Vulnerability (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2022-20653 and fix it if it is affected.

What it is: CVE-2022-20653 is a high-severity denial of service vulnerability in Cisco Asyncos, published on 17 Feb 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-2022-20653 in the wild and no public exploit code.

Affected product: Cisco Asyncos. 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-2022-20653/ (Markdown: https://insights.sbomify.com/CVE-2022-20653/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2022-20653
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2022-20653
- OSV: https://osv.dev/vulnerability/CVE-2022-20653

---
From sbomify Insights: https://insights.sbomify.com/CVE-2022-20653/
Summaries are generated and may contain mistakes; the official description above is the record.