CVE-2020-26138 — framework
MEDIUMCVE-2020-26138 is a medium-severity (CVSS 5.3) Improper Input Validation vulnerability in silverstripe/framework. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for silverstripe/framework — see the affected versions and patch details below.
FormField with square brackets in field name skips validation
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
silverstripe/frameworkReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
FileField with array notation skips validation
The FileField class is commonly used for file upload in custom code on a Silverstripe website. This field is designed to be used with a single file upload.
PHP allows for submitting multiple values by adding square brackets to the field name. When this is done to a FileField, it will be coerced into allowing multiple files by using this notation. This is not a supported feature, though nothing is done to prevent this.
In this scenario, validation such as limiting allowed extensions is not applied, and the FileField->saveInto() behaviour is not triggered. If custom controller logic is used to process the file uploads, it might implicitly rely on validation to be provided by the Form system, which is not the case.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | silverstripe/framework | ≥ 3.0.0&&< 4.7.4 | 4.7.4composer require silverstripe/framework:^4.7.4 |
Affected Products
silverstripesilverstripeResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for silverstripe/framework, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update silverstripe/framework to 4.7.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-26138 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2020-26138 in your dependencies?
Find it across Packagist, including transitive dependencies.