CVE-2026-100859 in Heym
Summary
by MITRE • 09/27/2026
Heym before 0.0.106 contains a credential exfiltration vulnerability in the POST /api/credentials/test endpoint that allows collaborators with shared credential access to exfiltrate the credential owner's secret. Attackers can override the destination URL in the config parameter to cause the server to send decrypted authentication secrets to attacker-controlled endpoints.
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Analysis
by VulDB Data Team • 09/27/2026
The Heym application, prior to version 0.0.106, contains a critical security flaw within its API endpoint responsible for testing credential configurations. This vulnerability specifically affects the POST /api/credentials/test route and represents a significant breach of confidentiality due to improper access control mechanisms governing how shared credentials are processed during validation operations. The core technical issue stems from an insecure direct object reference combined with insufficient input validation on the configuration parameters passed by authenticated users who have been granted collaborative access rights.
When a user with shared credential access initiates a test operation, the application processes the provided configuration data to verify connectivity or authentication success against target services. However, the implementation fails to restrict the destination URL specified in the config parameter to only allow connections to legitimate, intended targets. Instead, it permits arbitrary URLs to be supplied by the client side of the request. This lack of validation allows an attacker who has been granted collaborative access to a shared credential entry to manipulate this field during the test execution phase.
The operational impact of this vulnerability is severe because it enables unauthorized exfiltration of sensitive authentication secrets. By overriding the destination URL in the config parameter, an attacker can direct the server to send decrypted credentials and other secret values back to endpoints controlled by the adversary. This occurs because the testing mechanism likely transmits the full credential payload as part of its diagnostic or verification process when interacting with external services. Consequently, even though the attacker does not have direct read access to view the secrets within the application interface, they can trigger a server-side action that leaks these plaintext values over the network.
This behavior aligns closely with CWE-209, which describes the generation of an error message that reveals sensitive information, and more specifically CWE-359 regarding exposure of private information through side channels or unintended data transmission. From an ATT&CK perspective, this vulnerability facilitates Credential Access techniques such as T1078 Valid Accounts, where attackers leverage legitimate credentials to gain access, but in this case, it extends into active exfiltration via T1041 Exfiltration Over C2 Channel if the attacker controls the receiving endpoint. The flaw essentially turns a diagnostic feature into an attack vector for data theft without requiring additional privilege escalation beyond existing collaborative permissions.
Mitigation strategies must focus on strict input validation and output encoding practices within the API layer. Developers should implement allow-listing for destination URLs to ensure that only predefined, trusted hosts can be contacted during credential testing operations. Additionally, implementing a proxy or sandboxed environment for outbound network requests from server-side test functions would prevent direct communication with arbitrary external endpoints. It is also recommended to avoid transmitting full plaintext secrets in diagnostic payloads unless absolutely necessary and encrypted end-to-end regardless of the destination. Upgrading Heym to version 0.0.106 or later resolves this issue by addressing these validation gaps. Organizations relying on earlier versions should immediately restrict collaborative access privileges until patches are applied, as any user with shared credential rights can exploit this flaw to steal sensitive authentication data from other collaborators.