# CVE-2020-26276: SAML authentication vulnerability in Fleet

> Attackers can bypass SAML authentication in Fleet by mutating XML responses, allowing unverified logins when SSO is enabled.

- **Severity:** Critical 10.0 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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:** Yes
- **Published:** 17 Dec 2020
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-w3wf-cfx3-6gcx

## What is CVE-2020-26276?

CVE-2020-26276 is a critical authentication bypass vulnerability in fleetdm fleet, published on 17 Dec 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Fleet is an open source osquery manager. In Fleet before version 3.5.1, due to issues in Go's standard library XML parsing, a valid SAML response may be mutated by an attacker to modify the trusted document. This can result in allowing unverified logins from a SAML IdP. Users that configure Fleet with SSO login may be vulnerable to this issue. This issue is patched in 3.5.1. The fix was made using https://github.com/mattermost/xml-roundtrip-validator If upgrade to 3.5.1 is not possible, users should disable SSO authentication in Fleet.

Weakness: CWE-290 (Authentication Bypass by Spoofing)

## Which versions are affected by CVE-2020-26276?

2 open source packages ship an affected version, including github.com/fleetdm/fleet/v4. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/fleetdm/fleet/v4` | Go | All versions | 3.5.1 |
| `github.com/fleetdm/fleet/v4` | Go | All versions | 3.5.1 |

Products: Fleetdm Fleet.

## How do I fix CVE-2020-26276?

Upgrade github.com/fleetdm/fleet/v4 to 3.5.1 or later.

## Is CVE-2020-26276 being exploited?

There is no known exploitation of CVE-2020-26276 in the wild and no public exploit code.

## Other vulnerabilities in fleetdm fleet

- [CVE-2026-103264](https://insights.sbomify.com/CVE-2026-103264/): Fleet before 4.87.0 Authentication Bypass via Device Identifiers (critical 9.3)
- [CVE-2026-23518](https://insights.sbomify.com/CVE-2026-23518/): Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment (critical 9.3)
- [CVE-2026-26062](https://insights.sbomify.com/CVE-2026-26062/): Fleet server may terminate unexpectedly when handling certain gRPC requests (high 8.7)
- [CVE-2026-26061](https://insights.sbomify.com/CVE-2026-26061/): Fleet's unbounded request body read allows remote Denial of Service (high 8.7)
- [CVE-2026-23998](https://insights.sbomify.com/CVE-2026-23998/): Fleet has a Windows MDM management endpoint authentication bypass (high 8.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-26276 and fix it if it is affected.

What it is: CVE-2020-26276 is a critical authentication bypass vulnerability in fleetdm fleet, published on 17 Dec 2020. 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-2020-26276 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/fleetdm/fleet/v4 (Go): affected all versions; fixed in 3.5.1
- github.com/fleetdm/fleet/v4 (Go): affected all versions; fixed in 3.5.1

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-2020-26276/ (Markdown: https://insights.sbomify.com/CVE-2020-26276/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-26276
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-26276
- OSV: https://osv.dev/vulnerability/CVE-2020-26276

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-26276/
Summaries are generated and may contain mistakes; the official description above is the record.