# CVE-2023-20042: Denial of service in Cisco Adaptive Security Appliance (ASA) Software

> Unauthenticated remote attackers can cause a denial of service by depleting session handlers via crafted SSL/TLS traffic in Cisco ASA and FTD devices.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/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:** 1 Nov 2023
- **Updated:** 2 Aug 2024
- **Also known as:** GHSA-2c63-fqw2-3fhm

## What is CVE-2023-20042?

CVE-2023-20042 is a medium-severity denial of service vulnerability in Cisco Adaptive Security Appliance Software, published on 1 Nov 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the AnyConnect SSL VPN feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to an implementation error within the SSL/TLS session handling process that can prevent the release of a session handler under specific conditions. An attacker could exploit this vulnerability by sending crafted SSL/TLS traffic to an affected device, increasing the probability of session handler leaks. A successful exploit could allow the attacker to eventually deplete the available session handler pool, preventing new sessions from being established and causing a DoS condition.

Weakness: CWE-404 (Improper Resource Shutdown or Release)

## Which versions are affected by CVE-2023-20042?

It affects 2 products.


Products: Cisco Adaptive Security Appliance Software, Cisco Secure Firewall Threat Defense.

## How do I fix CVE-2023-20042?

No fix has been published for CVE-2023-20042 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-20042 being exploited?

There is no known exploitation of CVE-2023-20042 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Adaptive Security Appliance Software

- [CVE-2025-20333](https://insights.sbomify.com/CVE-2025-20333/): Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow (critical 9.9, exploited in the wild)
- [CVE-2016-6366](https://insights.sbomify.com/CVE-2016-6366/): Cisco Adaptive Security Appliance (ASA) SNMP Buffer Overflow (high 8.8, exploited in the wild)
- [CVE-2026-20349](https://insights.sbomify.com/CVE-2026-20349/): Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Heap Inspection (high 8.6, exploited in the wild)
- [CVE-2024-20353](https://insights.sbomify.com/CVE-2024-20353/): Cisco ASA and FTD Denial of Service (high 8.6, exploited in the wild)
- [CVE-2016-6367](https://insights.sbomify.com/CVE-2016-6367/): Cisco Adaptive Security Appliance (ASA) CLI Remote Code Execution (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-20042 and fix it if it is affected.

What it is: CVE-2023-20042 is a medium-severity denial of service vulnerability in Cisco Adaptive Security Appliance Software, published on 1 Nov 2023. 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-2023-20042 in the wild and no public exploit code.

Affected product: Cisco Adaptive Security Appliance Software. 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-2023-20042/ (Markdown: https://insights.sbomify.com/CVE-2023-20042/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-20042
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-20042
- OSV: https://osv.dev/vulnerability/CVE-2023-20042

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-20042/
Summaries are generated and may contain mistakes; the official description above is the record.