# CVE-2020-26138: FormField with square brackets in field name skips validation

> Attackers can bypass form validation by using square brackets in field names, potentially submitting invalid or malicious data.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Jun 2021
- **Updated:** 4 Aug 2024
- **Also known as:** BIT-silverstripe-2020-26138, GHSA-7mv4-4xpg-xq44

## What is CVE-2020-26138?

CVE-2020-26138 is a medium-severity missing authorization vulnerability in Silverstripe Silverstripe, published on 8 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In SilverStripe through 4.6.0-rc1, a FormField with square brackets in the field name skips validation.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2020-26138?

3 open source packages ship an affected version, including silverstripe/framework and silverstripe. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `silverstripe/framework` | Packagist | From 3.0.0 | 4.7.4 |
| `silverstripe/framework` | Packagist | From 3.0.0 | 4.7.4 |
| `silverstripe` | Bitnami | All versions to 4.6.0-rc1 | 4.6.0 |

Products: Silverstripe Silverstripe.

## How do I fix CVE-2020-26138?

Upgrade silverstripe/framework to 4.7.4 or later.

## Is CVE-2020-26138 being exploited?

There is no known exploitation of CVE-2020-26138 in the wild and no public exploit code.

## Other vulnerabilities in Silverstripe Silverstripe

- [CVE-2007-2321](https://insights.sbomify.com/CVE-2007-2321/): Other in n/a (critical 10.0)
- [CVE-2019-12204](https://insights.sbomify.com/CVE-2019-12204/): Missing warning can lead to unauthenticated admin access in SilverStripe (critical 9.8)
- [CVE-2019-5715](https://insights.sbomify.com/CVE-2019-5715/): Silverstripe Framework SQLi Vulnerability (critical 9.8)
- [CVE-2019-12437](https://insights.sbomify.com/CVE-2019-12437/): Silverstripe CSRF Protection Bypass via GraphQL (high 8.8)
- [CVE-2020-6164](https://insights.sbomify.com/CVE-2020-6164/): Silverstripe CMS information disclosure (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-26138 and fix it if it is affected.

What it is: CVE-2020-26138 is a medium-severity missing authorization vulnerability in Silverstripe Silverstripe, published on 8 Jun 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-2020-26138 in the wild and no public exploit code.

Affected packages and fixed versions:
- silverstripe/framework (Packagist): affected from 3.0.0; fixed in 4.7.4
- silverstripe/framework (Packagist): affected from 3.0.0; fixed in 4.7.4
- silverstripe (Bitnami): affected all versions up to 4.6.0-rc1; fixed in 4.6.0

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-2020-26138/ (Markdown: https://insights.sbomify.com/CVE-2020-26138/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-26138
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-26138
- OSV: https://osv.dev/vulnerability/CVE-2020-26138

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From sbomify Insights: https://insights.sbomify.com/CVE-2020-26138/
Summaries are generated and may contain mistakes; the official description above is the record.