# CVE-2026-20028: Cisco Terminal Services Agent Firewall Rules Bypass Vulnerability

> An authenticated attacker can bypass firewall rules by exploiting incorrect network connection mapping in Cisco Terminal Services Agent.

- **Severity:** Medium 5.0 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 5 Aug 2026
- **Updated:** 5 Aug 2026
- **Also known as:** GHSA-6vj9-8q5m-xjpv

## What is CVE-2026-20028?

CVE-2026-20028 is a medium-severity vulnerability in Cisco Terminal Services Agent, published on 5 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A vulnerability in the network driver of Cisco Terminal Service (TS) Agent could allow an authenticated, remote attacker to bypass firewall rules that are associated with the account of the attacker.

This vulnerability is due to an incorrect mapping of network connections to user accounts. An attacker with at least user-level credentials could exploit this vulnerability by sending crafted network traffic to an affected device. A successful exploit could allow the attacker to inherit the firewall rules associated with a different user in the system.

Weakness: CWE-266 (Incorrect Privilege Assignment)

## Which versions are affected by CVE-2026-20028?


## How do I fix CVE-2026-20028?

No fix has been published for CVE-2026-20028 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-20028 being exploited?

There is no known exploitation of CVE-2026-20028 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-20028 and fix it if it is affected.

What it is: CVE-2026-20028 is a medium-severity vulnerability in Cisco Terminal Services Agent, published on 5 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-20028 in the wild and no public exploit code.

Affected product: Cisco Terminal Services Agent. 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-2026-20028/ (Markdown: https://insights.sbomify.com/CVE-2026-20028/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-20028
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20028
- OSV: https://osv.dev/vulnerability/CVE-2026-20028

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-20028/
Summaries are generated and may contain mistakes; the official description above is the record.