# CVE-2025-20271: Cisco Meraki MX and Z Series AnyConnect VPN with Client Certificate Authentication Denial of Service Vulnerability

> Unauthenticated remote attackers can cause a denial of service in Cisco Meraki AnyConnect VPN by sending crafted HTTPS requests, disrupting all active sessions.

- **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:** 18 Jun 2025
- **Updated:** 18 Jun 2025
- **Also known as:** GHSA-m673-qg9w-p8mh

## What is CVE-2025-20271?

CVE-2025-20271 is a high-severity denial of service vulnerability in Cisco Meraki MX Firmware, published on 18 Jun 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the Cisco AnyConnect VPN server of Cisco Meraki MX and Cisco Meraki Z Series Teleworker Gateway devices could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition in the Cisco AnyConnect service on an affected device.

This vulnerability is due to variable initialization errors when an SSL VPN session is established. An attacker could exploit this vulnerability by sending a sequence of crafted HTTPS requests to an affected device. A successful exploit could allow the attacker to cause the Cisco AnyConnect VPN server to restart, resulting in the failure of all established SSL VPN sessions and forcing remote users to initiate a new VPN connection and re-authenticate. A sustained attack could prevent new SSL VPN connections from being established, effectively making the Cisco AnyConnect VPN service unavailable for all legitimate users.

Weakness: CWE-457 (Use of Uninitialized Variable)

## Which versions are affected by CVE-2025-20271?


## How do I fix CVE-2025-20271?

No fix has been published for CVE-2025-20271 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-20271 being exploited?

There is no known exploitation of CVE-2025-20271 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-20271 and fix it if it is affected.

What it is: CVE-2025-20271 is a high-severity denial of service vulnerability in Cisco Meraki MX Firmware, published on 18 Jun 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-2025-20271 in the wild and no public exploit code.

Affected product: Cisco Meraki MX Firmware. 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-2025-20271/ (Markdown: https://insights.sbomify.com/CVE-2025-20271/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-20271
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-20271
- OSV: https://osv.dev/vulnerability/CVE-2025-20271

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-20271/
Summaries are generated and may contain mistakes; the official description above is the record.