CVE-2026-56309 in Capgo
Summary
by MITRE • 07/10/2026
Capgo before 12.128.2 fails to enforce plan/quota restrictions on the /files/upload/attachments endpoint, allowing plan-blocked apps to create publicly readable R2 objects. Attackers can upload arbitrary attachments using upload-scoped API keys that bypass plan checks, persist outside normal bundle metadata, and survive app deletion, enabling storage and bandwidth abuse.
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Analysis
by VulDB Data Team • 07/10/2026
The vulnerability in Capgo versions prior to 12.128.2 represents a critical authorization flaw that undermines the platform's resource management controls. This issue specifically affects the /files/upload/attachments endpoint where the system fails to properly validate plan restrictions and quota limitations that should normally prevent plan-blocked applications from performing certain operations. The flaw exists at the application layer where access control mechanisms are bypassed, allowing unauthorized operations to proceed despite contractual or subscription-based limitations that should normally restrict such activities.
The technical implementation of this vulnerability stems from insufficient input validation and authorization checks within the upload endpoint. When applications attempt to upload attachments through upload-scoped API keys, the system does not properly verify whether the requesting application is permitted to perform such operations based on its current plan status. This creates a scenario where malicious actors can leverage valid upload credentials to bypass normal security boundaries that would typically restrict resource consumption based on subscription tiers.
The operational impact of this vulnerability extends beyond simple unauthorized file uploads and creates persistent storage abuse opportunities. Uploaded files become publicly readable R2 objects that persist indefinitely outside the normal lifecycle of application bundles, meaning they survive even when the original application is deleted or deactivated. This characteristic transforms what could be a temporary security issue into a long-term resource consumption problem that can generate significant bandwidth and storage costs for the platform operator while potentially exposing sensitive data through publicly accessible files.
The vulnerability aligns with CWE-639 Access Control Bypass, specifically addressing weak authorization checks where the system fails to properly validate user permissions before allowing access to restricted resources. From an adversary perspective, this represents a sophisticated attack vector that leverages legitimate API key usage patterns to circumvent normal security controls while maintaining persistence through the R2 storage system's object lifecycle management. The ATT&CK framework categorizes this as privilege escalation and resource consumption abuse, where attackers can amplify their impact by utilizing valid credentials to perform unauthorized operations with persistent effects.
Mitigation strategies should focus on implementing comprehensive authorization checks at the endpoint level, ensuring that all upload operations validate both the API key scope and the associated application's plan restrictions. The system must enforce quota validation for each upload request regardless of credential type, and implement proper access control lists that prevent publicly readable object creation when plan limitations are in place. Additionally, the platform should establish monitoring mechanisms to detect unusual upload patterns that exceed normal application behavior, combined with automated cleanup procedures for orphaned objects that persist after application deletion to prevent long-term abuse.