CVE-2026-100617 in Capgo.app
Summary
by MITRE • 09/26/2026
Cap-go capgo.app fails to validate that principals in channel_permission_overrides belong to the organization, allowing authenticated app/org admins to grant channel permissions to non-member users. Attackers with admin privileges can insert override rows with arbitrary external user UUIDs to grant channel-scoped permissions such as channel.promote_bundle to users outside the organization.
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Analysis
by VulDB Data Team • 09/26/2026
The vulnerability identified in Cap-go represents a critical authorization flaw within the application's permission management system, specifically targeting the channel_permission_overrides functionality. This issue stems from an insufficient validation mechanism when processing requests that modify access control lists for specific channels. The core technical deficiency lies in the backend logic which fails to verify whether the principal identifiers provided in override rows are actually members of the organization associated with the targeted channel. By omitting this crucial membership check, the system allows authenticated administrators who possess elevated privileges within an organization to bypass standard organizational boundaries and assign permissions to external entities that have no legitimate affiliation with the group.
From a technical perspective, this flaw constitutes a classic case of Broken Access Control where the application relies on implicit trust in administrative actions without enforcing strict boundary checks against data integrity constraints. An attacker who has compromised or been granted admin privileges within an organization can exploit this by injecting override rows containing arbitrary external user UUIDs into the permission database. These overrides effectively grant channel-scoped permissions, such as channel.promote_bundle, to users outside the organization's membership roster. This manipulation allows the creation of unauthorized access paths that circumvent standard authentication and authorization protocols designed to isolate organizational data and resources from external influence.
The operational impact of this vulnerability is significant for organizations relying on Cap-go for secure collaboration or resource management. By granting permissions to non-member users, attackers can potentially escalate their privileges within specific channels, leading to unauthorized modifications of channel settings, exfiltration of sensitive information contained within those channels, or further lateral movement if the external user accounts are linked to other compromised systems. This undermines the fundamental security principle that administrative actions should respect organizational boundaries and ensures that only verified members can influence channel-specific configurations. The ability to promote bundles or alter permissions externally creates a backdoor-like effect where internal controls are rendered ineffective by simple data injection techniques.
This vulnerability aligns with CWE-269, which describes Improper Privilege Management, as it involves the misuse of administrative privileges to grant unauthorized access rights. Furthermore, in the context of the MITRE ATT&CK framework, this behavior corresponds to T1078 Valid Accounts and potentially T1548 Abuse Elevation Control Mechanism, where an attacker uses legitimate credentials with elevated permissions to bypass security restrictions. The exploitation vector is straightforward for any authenticated admin, making it a high-risk issue that requires immediate remediation through code changes rather than configuration adjustments alone.
To mitigate this vulnerability, developers must implement strict validation logic within the channel_permission_overrides endpoint or service layer. This involves querying the organization's membership database to confirm that every principal UUID included in an override request is indeed a verified member of the target organization before persisting any permission changes. Additionally, implementing comprehensive audit logging for all privilege modification events will aid in detecting such anomalies post-exploitation. Regular security code reviews focusing on authorization checks and input validation are essential to prevent similar flaws from being introduced during future development cycles.