# CVE-2021-26088: Auth bypass in Fortinet FSSO Windows DC Agent, FSSO Windows CA

> Unauthenticated attackers can bypass firewall policies and access protected networks by sending crafted UDP packets to the FSSO Collector.

- **Severity:** High 7.1 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Jul 2021
- **Updated:** 25 Oct 2024
- **Also known as:** GHSA-pp6p-mhjc-6vgp

## What is CVE-2021-26088?

CVE-2021-26088 is a high-severity authentication bypass vulnerability in Fortinet FSSO Windows DC Agent, FSSO Windows CA, published on 12 Jul 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

An improper authentication vulnerability in FSSO Collector version 5.0.295 and below may allow an unauthenticated user to bypass a FSSO firewall policy and access the protected network via sending specifically crafted UDP login notification packets.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2021-26088?

It affects 1 product.


Products: Fortinet Fortinet Single Sign-On.

## How do I fix CVE-2021-26088?

No fix has been published for CVE-2021-26088 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-26088 being exploited?

There is no known exploitation of CVE-2021-26088 in the wild and no public exploit code.

Public exploit code:

- PoC for CVE-2021-26088 written in PowerShell (github_poc): https://github.com/theogobinet/CVE-2021-26088

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-26088 and fix it if it is affected.

What it is: CVE-2021-26088 is a high-severity authentication bypass vulnerability in Fortinet FSSO Windows DC Agent, FSSO Windows CA, published on 12 Jul 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-26088 in the wild and no public exploit code.

Affected product: Fortinet FSSO Windows DC Agent, FSSO Windows CA. 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-2021-26088/ (Markdown: https://insights.sbomify.com/CVE-2021-26088/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-26088
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-26088
- OSV: https://osv.dev/vulnerability/CVE-2021-26088

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-26088/
Summaries are generated and may contain mistakes; the official description above is the record.