# CVE-2026-59243: Auth bypass in Apache Airflow FAB provider

> Attackers can bypass authentication and log in as arbitrary users, including admins, due to disabled JWT signature verification in Azure AD OAuth.

- **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:** Yes
- **Published:** 29 Jul 2026
- **Updated:** 16 Sep 2026
- **Also known as:** CLEANSTART-2026-LK77768, GHSA-q5r3-w69r-hrfw

## What is CVE-2026-59243?

CVE-2026-59243 is a critical authentication bypass vulnerability in Apache Airflow FAB provider, published on 29 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The FAB auth manager's Azure AD OAuth login defaulted `verify_signature=False` when decoding the ID token, so an attacker able to present a forged or unsigned (`alg:none`) ID token to the OAuth callback could bypass authentication and log in as an arbitrary user, including one holding the Admin role (CWE-347). Deployments running the FAB auth manager with the Azure AD OAuth login path under its default configuration are affected; the Authentik path already defaulted to `True`. This issue affects `apache-airflow-providers-fab` before 3.7.3. Users are advised to upgrade to `apache-airflow-providers-fab` 3.7.3, which defaults `verify_signature=True`.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-59243?

It affects 1 product.


Products: Apache Apache-Airflow-Providers-Fab.

## How do I fix CVE-2026-59243?

Upgrade to a fixed version.

## Is CVE-2026-59243 being exploited?

There is no known exploitation of CVE-2026-59243 in the wild and no public exploit code.

Public exploit code:

- https://github.com/0xdak/CVE-2026-59243_exploit (github_poc): https://github.com/0xdak/CVE-2026-59243_exploit
- CVE-2026-59243 — Apache Airflow FAB Auth Manager JWT signature bypass (embargoed until Apache advisory) (github_poc): https://github.com/MalHyuk/CVE-2026-59243

## Other vulnerabilities in Apache Airflow FAB provider

- [CVE-2026-82311](https://insights.sbomify.com/CVE-2026-82311/): Security feature bypass in Apache Airflow FAB provider (critical 9.8)
- [CVE-2024-42447](https://insights.sbomify.com/CVE-2024-42447/): Apache Airflow Providers FAB: FAB provider 1.2.1 and 1.2.0 did not let user to logout for Airflow (critical 9.8)
- [CVE-2026-86462](https://insights.sbomify.com/CVE-2026-86462/): Apache Airflow FAB provider: FAB Admin password PATCH does not invalidate database-backed sessions (critical 9.1)
- [CVE-2026-75156](https://insights.sbomify.com/CVE-2026-75156/): Auth bypass in Apache Airflow FAB provider (critical 9.1)
- [CVE-2026-86466](https://insights.sbomify.com/CVE-2026-86466/): Apache Airflow FAB provider: FAB Authentik provider: id_token issuer/audience not validated (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-59243 and fix it if it is affected.

What it is: CVE-2026-59243 is a critical authentication bypass vulnerability in Apache Airflow FAB provider, published on 29 Jul 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-2026-59243 in the wild and no public exploit code.

Affected product: Apache Airflow FAB provider. 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-2026-59243/ (Markdown: https://insights.sbomify.com/CVE-2026-59243/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-59243
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59243
- OSV: https://osv.dev/vulnerability/CVE-2026-59243

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-59243/
Summaries are generated and may contain mistakes; the official description above is the record.