CVE-2020-9309

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2020-07-15 · updated 2026-06-17
Weakness: CWE-434

Description

Silverstripe CMS through 4.5 can be susceptible to script execution from malicious upload contents under allowed file extensions (for example HTML code in a TXT file). When these files are stored as protected or draft files, the MIME detection can cause browsers to execute the file contents. Uploads stored as protected or draft files are allowed by default for authorised users only, but can also be enabled through custom logic as well as modules such as silverstripe/userforms. Sites using the previously optional silverstripe/mimevalidator module can configure MIME whitelists rather than extension whitelists, and hence prevent this issue. Sites on the Common Web Platform (CWP) use this module by default, and are not affected.

Affected products

silverstripe Mimevalidator: before 2.0.0 — fixed in 2.0.0
silverstripe Recipe: from 4.0.0 before 4.6.0 — fixed in 4.6.0

How to fix

Upgrade to a fixed version: silverstripe Mimevalidator 2.0.0; silverstripe Recipe 4.6.0. Check the vendor advisory for mitigations.

References

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