# CVE-2026-20242: Cisco Secure Firewall Management Center Software Java Deserialization Remote Code Execution Vulnerability

> Unauthenticated remote attackers can execute arbitrary commands as root via insecure Java deserialization in Cisco FMC if they control a host in the external database access list.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 16 Sep 2026
- **Updated:** 18 Sep 2026
- **Also known as:** GHSA-mgpv-rwhr-9mx2

## What is CVE-2026-20242?

CVE-2026-20242 is a critical unsafe deserialization vulnerability in Cisco Secure Firewall Management Center (FMC), published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the External Database Access feature of Cisco Secure Firewall Management Center (FMC) Software could allow an unauthenticated, remote attacker to execute arbitrary commands as root on an affected device.

This vulnerability is due to insecure deserialization of a user-supplied Java byte stream from a host that is configured in the external database access list. An attacker could exploit this vulnerability by sending a crafted, serialized Java byte stream to a specific TCP port of an affected device. A successful exploit could allow the attacker to execute arbitrary commands on the device and elevate privileges to root.
Notes:

This vulnerability can be exploited only by an attacker who has control of a host in the external database access list.
If the FMC management interface does not have public internet access, the attack surface that is associated with this vulnerability is reduced.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2026-20242?


## How do I fix CVE-2026-20242?

No fix has been published for CVE-2026-20242 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-20242 being exploited?

There is no known exploitation of CVE-2026-20242 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-20242 and fix it if it is affected.

What it is: CVE-2026-20242 is a critical unsafe deserialization vulnerability in Cisco Secure Firewall Management Center (FMC), published on 16 Sep 2026. 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-2026-20242 in the wild and no public exploit code.

Affected product: Cisco Secure Firewall Management Center (FMC). 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-2026-20242/ (Markdown: https://insights.sbomify.com/CVE-2026-20242/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-20242
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20242
- OSV: https://osv.dev/vulnerability/CVE-2026-20242

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-20242/
Summaries are generated and may contain mistakes; the official description above is the record.