CVE-2026-85700 in Onyx
Summary
by MITRE • 09/04/2026
Onyx 4.6.6 fails to properly restrict access to custom tool credentials stored in custom_headers, allowing any authenticated user to read admin-defined API keys. Attackers with basic authentication can call GET /tool/{tool_id} or GET /tool endpoints to retrieve plaintext authorization headers and third-party API credentials, then use them to directly access upstream APIs.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified in Onyx version 4.6.6 represents a critical failure in access control mechanisms regarding sensitive credential storage. Specifically, the application fails to properly restrict access to custom tool credentials that are stored within the custom_headers configuration structure. This architectural flaw allows any authenticated user, regardless of their privilege level or role assignment, to retrieve administrative-defined API keys and third-party service tokens. The core issue lies in the lack of proper authorization checks when serving data related to configured tools, effectively treating sensitive security material as publicly accessible content for all logged-in users rather than restricting it to system administrators only.
From a technical perspective, this flaw manifests through specific HTTP endpoints designed for tool management and retrieval. Attackers possessing basic authentication credentials can exploit the GET /tool/{tool_id} or GET //tool endpoints to extract plaintext authorization headers. These responses contain sensitive information such as API keys required by upstream services integrated with Onyx. Because these credentials are returned in clear text within the HTTP response body, there is no encryption at rest or in transit protection for this specific data class during retrieval operations. This exposure enables an attacker to directly consume the stolen tokens against the respective third-party APIs that rely on them for authentication and authorization.
The operational impact of this vulnerability is severe due to its potential for lateral movement and privilege escalation within integrated ecosystems. By obtaining valid API keys, an authenticated user can impersonate the system or specific service accounts when interacting with upstream providers. This capability allows unauthorized access to external data stores, manipulation of third-party services, or execution of actions that should be restricted to administrative roles only. In environments where Onyx serves as a gateway or aggregator for multiple SaaS applications, this breach compromises not just the internal application but also the integrity and confidentiality of all connected upstream systems. The attacker can perform actions such as reading sensitive data from external databases, modifying configurations in third-party platforms, or potentially exfiltrating customer information depending on the permissions granted to those API keys.
This vulnerability aligns with CWE-284 Improper Access Control, specifically reflecting a failure to enforce proper authorization checks for critical resources. It also maps directly to MITRE ATT&CK technique T1078 Valid Accounts, as it involves using legitimate credentials to access unauthorized data, and potentially T1539 Steal Web Session Cookie if session tokens are included in the exposed headers. The scenario illustrates a classic case of broken object level authorization where resource identifiers are accessible without verifying that the requesting user has permission to view those specific objects or their associated metadata.
To mitigate this risk, immediate remediation should focus on implementing strict role-based access control for all endpoints returning sensitive configuration data. Administrators must ensure that GET requests for tool configurations and custom headers return empty values or masked credentials unless the requester holds an explicit administrative role. Additionally, security controls such as attribute-based access control can be applied to validate user permissions before serializing response objects containing secrets. It is also recommended to rotate all exposed API keys immediately upon confirmation of exploitation, as passive exposure may have already occurred in unpatched environments. Future development cycles should incorporate automated testing for authorization flaws using tools that simulate unauthorized access attempts against credential-retrieval endpoints to prevent regression.