CVE-2020-26138 in SilverStripe
Summary
by MITRE • 06/09/2021
In SilverStripe through 4.6.0-rc1, a FormField with square brackets in the field name skips validation.
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Analysis
by VulDB Data Team • 06/11/2021
The vulnerability identified as CVE-2020-26138 affects SilverStripe content management systems through version 4.6.0-rc1, representing a critical validation bypass flaw that undermines the integrity of form processing mechanisms. This issue specifically targets FormField components where field names contain square brackets, creating a condition that allows validation rules to be completely ignored during form submission processes.
The technical root cause of this vulnerability stems from how SilverStripe's form validation system processes field names containing square brackets. These characters are commonly used in HTML forms to denote array structures, particularly when multiple values need to be submitted under a single field name. When a FormField is configured with square brackets in its name, the validation logic fails to properly parse or recognize the field, resulting in the system skipping validation entirely for that particular field regardless of the validation rules that should be applied.
This flaw operates at the application logic level and can be categorized under CWE-692 - Improper Handling of Incomplete Input, which specifically addresses situations where applications fail to properly handle input that does not conform to expected formats. The vulnerability creates a pathway for malicious actors to bypass critical validation controls that are designed to ensure data integrity and prevent unauthorized access patterns.
The operational impact of this vulnerability extends beyond simple data validation failures, potentially enabling attackers to submit malformed or malicious data without triggering the security checks that should prevent such submissions. An attacker could exploit this by crafting form fields with square bracket notation to bypass validation rules that would normally prevent data injection attacks, cross-site scripting attempts, or other malicious input patterns. This creates a significant risk for applications that rely on SilverStripe's form validation to protect against common web application vulnerabilities.
The vulnerability aligns with several ATT&CK techniques including T1078 - Valid Accounts and T1213 - Data from Information Repositories, as it could enable unauthorized data manipulation or access to protected form processing mechanisms. Attackers could leverage this bypass to submit data that would normally be rejected, potentially leading to data corruption, unauthorized access, or exploitation of other vulnerabilities that depend on proper input validation.
Organizations using SilverStripe versions prior to 4.6.0-rc1 should immediately implement mitigations including upgrading to the patched version where validation logic has been corrected to properly handle square bracket characters in field names. Additionally, administrators should review all form configurations to identify any fields that might contain square brackets and ensure that proper validation is maintained through alternative means. The recommended approach involves implementing comprehensive input sanitization processes and thorough testing of form validation logic to prevent similar issues in custom implementations.