# CVE-2025-20133: Denial of service in Cisco Adaptive Security Appliance (ASA) Software

> Unauthenticated remote attackers can cause a denial of service in Cisco Secure Firewall ASA and FTD devices by sending crafted requests to the SSL VPN service.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/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:** 14 Aug 2025
- **Updated:** 14 Aug 2025
- **Also known as:** GHSA-5hvh-v86p-hc95

## What is CVE-2025-20133?

CVE-2025-20133 is a high-severity denial of service vulnerability in Cisco Adaptive Security Appliance (ASA) Software, published on 14 Aug 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the management and VPN web servers of the Remote Access SSL VPN feature of Cisco Secure Firewall ASA Software and Secure FTD Software could allow an unauthenticated, remote attacker to cause the device to unexpectedly stop responding, resulting in a DoS condition.

This vulnerability is due to ineffective validation of user-supplied input during the Remote Access SSL VPN authentication process. An attacker could exploit this vulnerability by sending a crafted request to the VPN service on an affected device. A successful exploit could allow the attacker to cause a DoS condition where the device stops responding to Remote Access SSL VPN authentication requests.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2025-20133?


## How do I fix CVE-2025-20133?

No fix has been published for CVE-2025-20133 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-20133 being exploited?

There is no known exploitation of CVE-2025-20133 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-20133 and fix it if it is affected.

What it is: CVE-2025-20133 is a high-severity denial of service vulnerability in Cisco Adaptive Security Appliance (ASA) Software, published on 14 Aug 2025. 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-2025-20133 in the wild and no public exploit code.

Affected product: Cisco Adaptive Security Appliance (ASA) 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-2025-20133/ (Markdown: https://insights.sbomify.com/CVE-2025-20133/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-20133
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-20133
- OSV: https://osv.dev/vulnerability/CVE-2025-20133

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-20133/
Summaries are generated and may contain mistakes; the official description above is the record.