# CVE-2020-27847: Auth bypass in dexidp/dex

> Attackers can bypass SAML authentication in the Dex library, compromising confidentiality, integrity, and availability.

- **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:** 28 May 2021
- **Updated:** 4 Aug 2024

## What is CVE-2020-27847?

CVE-2020-27847 is a critical authentication bypass vulnerability in dexidp/dex, published on 28 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability exists in the SAML connector of the github.com/dexidp/dex library used to process SAML Signature Validation. This flaw allows an attacker to bypass SAML authentication. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability. This flaw affects dex versions before 2.27.0.

Weakness: CWE-228 (Improper Handling of Syntactically Invalid Structure)

## Which versions are affected by CVE-2020-27847?

It affects 1 product.


Products: Linuxfoundation Dex.

## How do I fix CVE-2020-27847?

Upgrade to a fixed version.

## Is CVE-2020-27847 being exploited?

There is no known exploitation of CVE-2020-27847 in the wild and no public exploit code.

## Other vulnerabilities in dexidp/dex

- [CVE-2022-39222](https://insights.sbomify.com/CVE-2022-39222/): OAuth authorization code exposure in Dex (critical 9.3)
- [CVE-2020-26290](https://insights.sbomify.com/CVE-2020-26290/): Critical security issues in XML encoding in Dex (critical 9.3)
- [CVE-2024-23656](https://insights.sbomify.com/CVE-2024-23656/): Dex 2.37.0 is discarding TLSconfig and always serves deprecated TLS 1.0/1.1 and insecure ciphers (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-27847 and fix it if it is affected.

What it is: CVE-2020-27847 is a critical authentication bypass vulnerability in dexidp/dex, published on 28 May 2021. 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-2020-27847 in the wild and no public exploit code.

Affected product: dexidp/dex. 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-2020-27847/ (Markdown: https://insights.sbomify.com/CVE-2020-27847/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-27847
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-27847
- OSV: https://osv.dev/vulnerability/CVE-2020-27847

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-27847/
Summaries are generated and may contain mistakes; the official description above is the record.