Summary
FormField with square brackets in field name skips validation
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.
Impact
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
CVE-2020-26138 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.7.4); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2020-26138? CVE-2020-26138 is a medium-severity improper input validation vulnerability in silverstripe/framework (composer), affecting versions >= 3.0.0, < 4.7.4. It is fixed in 4.7.4. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- How severe is CVE-2020-26138? CVE-2020-26138 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of silverstripe/framework are affected by CVE-2020-26138? silverstripe/framework (composer) versions >= 3.0.0, < 4.7.4 is affected.
- Is there a fix for CVE-2020-26138? Yes. CVE-2020-26138 is fixed in 4.7.4. Upgrade to this version or later.
- Is CVE-2020-26138 exploitable, and should I be worried? Whether CVE-2020-26138 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2020-26138 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2020-26138? Upgrade
silverstripe/frameworkto 4.7.4 or later.