CVE-2026-33221 in Nhost
Summary
by MITRE • 03/21/2026
Nhost is an open source Firebase alternative with GraphQL. Prior to version 0.12.0, the storage service's file upload handler trusts the client-provided Content-Type header without performing server-side MIME type detection. This allows an attacker to upload files with an arbitrary MIME type, bypassing any MIME-type-based restrictions configured on storage buckets. This issue has been patched in version 0.12.0.
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Analysis
by VulDB Data Team • 06/04/2026
The vulnerability identified as CVE-2026-33221 affects Nhost, an open source platform designed as a Firebase alternative that provides GraphQL capabilities. This security flaw exists within the storage service's file upload handler functionality and represents a critical weakness in the platform's security architecture. The issue stems from the system's failure to properly validate and verify file metadata during the upload process, creating an opportunity for malicious actors to manipulate the system's behavior through crafted client requests.
The technical implementation of this vulnerability lies in the storage service's trust model for client-provided Content-Type headers during file uploads. When users upload files through the Nhost platform, the system accepts the Content-Type header directly from the client without performing any server-side MIME type detection or validation. This approach violates fundamental security principles of input validation and trust boundaries, as it allows attackers to submit any MIME type they choose regardless of the actual file content. The vulnerability directly maps to CWE-20, which addresses "Improper Input Validation" and specifically relates to the improper handling of untrusted data in security contexts.
The operational impact of this vulnerability extends beyond simple bypass of MIME type restrictions, creating potential pathways for more serious security breaches. Attackers can exploit this weakness to upload malicious files with deceptive MIME types that might bypass security scanning systems or be interpreted by web applications as safe content. This could enable various attack vectors including the execution of malicious scripts, bypassing of security filters, or exploitation of applications that make assumptions about file types based on Content-Type headers. The vulnerability particularly affects cloud storage services that rely on MIME type validation for access control, security scanning, or content delivery optimization.
The remediation for this vulnerability required implementing proper server-side MIME type detection and validation mechanisms within the storage service's file upload handler. Version 0.12.0 of Nhost introduced mandatory server-side content type verification that analyzes actual file signatures rather than relying on client-provided headers. This approach aligns with security best practices outlined in the OWASP Top Ten and follows the principle of least privilege by ensuring that server-side systems make authoritative decisions about file content rather than trusting potentially manipulated client data. The fix demonstrates the importance of defense in depth strategies where multiple layers of validation work together to prevent security bypasses. Organizations using Nhost should immediately upgrade to version 0.12.0 or later to mitigate this vulnerability and should also consider implementing additional monitoring for suspicious file upload patterns. The issue highlights the critical need for proper input sanitization and server-side validation in web applications, particularly those handling user-uploaded content where the integrity of file metadata directly impacts system security posture.